"PH drop": drop from what?

[Marwen]

Today, we all agree that the pH drop method is the best for estimating and profiling CO2 levels in our tanks.

However, I still to this day think that when we talk about a pH drop, there still isn't a universally agreed upon rule/practice for how we must all measure our starting pH.

This is despite it being extremely important for knowing our starting CO2 level. We need to have a good estimate for our starting CO2 concentration in order to know what our pH drop means.

Dennis Wong wrote the best guide on the topic. But he says to take a tank water sample, let it sit to degas, and assume it has 2-3 ppm (so the 1 pH drop from there is the rule of thumb). But is it really 2-3 from every tank? And is it 2 OR 3? How can I target specifically 20 versus 30 versus 40 ppm ?

Some reputable aquarists (like Marian Sterian for example) don't even seem to use the pH drop method and simply recommend to aim for a lime green drop checker.

Other masters of the art, like Tom, Joe and Gregg just go for a 1.4 pH drop (1.2 for Joe if I remember correctly). I'm curious to know from what they measure the starting pH.

What we know for sure is that a 1 pH drop = roughly x10 times the starting CO2 concentration, as part of a logarithmic scale.

So:

• If your starting CO2 is 0.6 ppm , a 1 pH drop = 6 ppm CO2
• If your starting CO2 is 1 ppm , a 1 pH drop = 10 ppm CO2
• If your starting CO2 is 2 ppm , a 1 pH drop = 20 ppm CO2
• If your starting CO2 is 3 ppm , a 1 pH drop = 30 ppm CO2

So with a 1 pH drop, knowing your starting CO2 could be the difference between having 6 and 30 ppm CO2. A huge difference.

Similarly, with a 1.4 pH drop:

• If your starting CO2 is 0.65 ppm , a 1.4 pH drop = 15 ppm CO2
• If your starting CO2 is 1 ppm , a 1.4 pH drop = 25 ppm CO2
• If your starting CO2 is 2 ppm , a 1.4 pH drop = 50 ppm CO2
• If your starting CO2 is 3 ppm , a 1.4 pH drop = 75 ppm CO2

What we know about the possible starting CO2 concentration:

1) The natural CO2 concentration in a biologically mature/active tank that is not CO2 injected can be anything from 2 ppm to 6 ppm (possibly more in tanks like Sudipta Shaw's, potentially as much as 10 ppm ). So taking a reading directly from a non-CO2-injected tank is one thing.

2) Taking a reading directly from CO2-injected tank at night or right before CO2 kicks in: the tank has the above + possibly still has residual CO2 from the previous photoperiod's CO2 injection. How much exactly is impossible to guess. So it's even more hard to predict.

3) Taking a sample of water from the tank and letting it sit for a day or two is yet another thing, it will come closer to equilibrium with the air but I believe that it still contains active microbiology from the tank and will likely now have less CO2 than the source tank but more CO2 than water that is fully in equilibrium with the air. Do we really know how much this concentration typically is and whether it varies widely from one tank to another?

4) Taking a sample of water from from the tank and running an air stone or some kind of mechanical agitation long enough for it to be brought into equilibrium with the air (you'll know it has reached that point when its pH stops rising beyond a certain point no matter how long you keep the agitation going), is yet another thing. I'm assuming that this overrides any biologically-generated CO2 and fully degasses it.

I use method #4 and then use this calculator (using the recommended Millero 2002 method since it's more accurate for biologically active freshwater systems) to estimate the CO2 concentration of my fully degassed tank water sample: https://www.hamzasreef.com/Contents/Calculators/CO2LevelFresh.php

I then use an excel sheet calculator that I made to figure out my target pH drop to reach my desired CO2 concentration (it simply uses the principle of: 1 pH drop = x10 times the initial CO2). Here are the results for my own tank:



So starting from my 0.65 ppm CO2 fully degassed water, I need a 1.7 pH drop from there to achieve 33 ppm CO2, and a 1.8 drop to achieve 40 ppm .

Am I missing something or am I incorrect about anything?

What I'd love to know specifically is whether that supposition is true or false: Mechanically agitating the tank water sample until its pH no longer rises no matter how much you try to agitate it does bring it into full equilibrium with the air. Because I don't see why it shouldn't.

If this is indeed true, then my method here is correct. If it's not true, then estimating the starting CO2 concentration is damn near impossible. And statements like "I have 30 ppm CO2 in this tank" are meaningless.

As you can see, the whole CO2 thing isn't easy when we're seeking accuracy, especially as far as trying to make it more accessible to a complete newbie. (Certainly not drop checker color game easy, but certainly more accurate, or so I hope.) Even after doing all of this work, this is still "an estimation". Because Millero 2002 itself is an estimation, albeit the best we have so far.

 

[Yugang]

Am I missing something or am I incorrect about anything?

I believe what many are missing is that it may not be important to know CO2 ppm accurately, as long as we keep it stable. As long as I know I have CO2 stable, can see that with pH profile, and know roughly where I am and see that confirmed with a drop checker, I really don't care if that is 30, 35 or 40 ppm .

The only correct reference for pH drop method is fully outgassed water. Following Henry's law partial CO2 pressure will be in equilibrium with ambient air (at about 400 ppm ). This, as you correctly say will give you around 0.6 ppm CO2 in the water.
Using tank water that has not been outgassed fully, is meaningless as a reference for pH drop method - full stop.

There are a couple of sources for error, and potentially big errors.

First, when we don't let the aquarium water outgas long enough we will not reach the equilibrium and can't be sure if indeed we are back to 0.6 ppm . I described in another thread CO2 pH reference - quick degassing how we can speed up the process, and when we know that we have reached the equilibrium point.

Second, and many make this mistake, we need to have equilibrium with the 400 ppm outdoor air. If we do the process indoor, where we could easilily have 1000 ppm or more, we will have probably a factor of two or more error in the assumption of 0.6 ppm . So when we drop pH by 1 from a 0.6 ppm sample, that we equilibrated outdoor, we get to 6 ppm , whereas if we would do it indoor we may be at 12 ppm or higher.

So, from the fact that we extraplolate, and do that with a logarithmic/exponential relationship is is very well possible that we have really big deviations from what we believe is correct. It is KEY that we correctly outgas.

Some reputable aquarists (like Marian Sterian for example) don't even seem to use the pH drop method and simply recommend to aim for a lime green drop checker.

This is always a good double check.

Dennis Wong wrote the best guide on the topic.

I agree it is a really good guide, as many articles on Dennis site. However, it would have been nice if @Dennis Wong had given credits to some of his sources.

 

[Pepere]

The only correct reference for pH drop method is fully outgassed water. Following Henry's law partial CO2 pressure will be in equilibrium with ambient air (at about 400 ppm ).

And in my bedroom where my tanks are after sleeping overnight with the windows closed and the bedroom door open, my ambient air will have a co2 level of 800-1500ppm depending on outside temperatures…

Even outside air as I live in the city near a busy road has co2 levels of around 500 ppm ….

I think people radically underestimate their indoor air co2 levels.

I go outside to degass my tank sample.

 

[Marwen]

Second, and many make this mistake, we need to have equilibrium with the 400 ppm outdoor air. If we do the process indoor, where we could easilily have 1000 ppm or more, we will have probably a factor of two or more error in the assumption of 0.6 ppm . So when we drop pH by 1 from a 0.6 ppm sample, that we equilibrated outdoor, we get to 6 ppm , whereas if we would do it indoor we may be at 12 ppm or higher.

And in my bedroom where my tanks are after sleeping overnight with the windows closed and the bedroom door open, my ambient air will have a co2 level of 800-1500ppm depending on outside temperatures…

Even outside air as I live in the city near a busy road has co2 levels of around 500 ppm ….

I think people radically underestimate their indoor air co2 levels.

I go outside to degass my tank sample.

I haven't thought of that before, nor encountered it in any CO2 posts/forums/articles.

I tried to confirm this today by degassing a tank sample outside (should be around 420 ppm at sea level where I am), and then inside the tank room.

I got pH 7.3 outside and the pH fell to 7.2 indoors, indicating higher CO2 levels indoors affecting equilibrium pH. I went back and forth a couple of times just to confirm and the effect was pretty obvious.

Learned something new today. Thanks!

 

[Marwen]

I believe what many are missing is that it may not be important to know CO2 ppm accurately, as long as we keep it stable. As long as I know I have CO2 stable, can see that with pH profile, and know roughly where I am and see that confirmed with a drop checker, I really don't care if that is 30, 35 or 40 ppm .

I agree, stability is key with CO2 due to plant adaptation to available CO2 levels. I don't care either if it's 30, 35 or 40 ppm . But not when it could be 6-30. That's too much uncertainty for me. And a hobbyist who follows the online guides using drop checkers or even using the 1 pH drop method can't be sure if he has 6 ppm (starting from 0.6 ppm ) or 30 ppm .

I like to be in the upper 30-40 ppm range personally because it helps stability. My logic is this: Let's say that we have a stability issue where CO2 is fluctuating up and down by 5 ppm . At 15 ppm , this fluctuation is 33% of the average CO2 level. Whereas at 35 ppm , this fluctuation is 14% of the total available CO2. (I think the same applies for nutrients that must always be available and that are safe to keep at higher amounts, like potassium.)

The only problem with higher CO2 levels is plants demand more nutrients and grow faster. And in a tank with many stem plants, it's a lot of labor. Not everyone's cup of tea for sure.

Good gear and injection methods affords us to keep more conservative but very stable CO2 levels.

Speaking of drop checkers, as Tom Barr says, the best way to use a drop checker is to throw it as hard as possible against a concrete floor. And then go buy a decent pH meter. lol

When I drop my pH correctly to get ~30 ppm in my zero KH tank, a drop checker using a typical 4dKH solution shows very strong yellow color, which the guides interpret as too much/toxic CO2. At 40 ppm it's almost orange. Fish and shrimp are fine, not even breathing hard.

 

[Yugang]

Good gear and injection methods affords us to keep more conservative but very stable CO2 levels.

Very true.

Speaking of drop checkers, as Tom Barr says, the best way to use a drop checker is to throw it as hard as possible against a concrete floor. And then go buy a decent pH meter. lol

Drop checker can be tricky, but pH meters have their own pro's and con's as well. The simplicity of drop checkers speaks for them, and I always use one as a double check to make sure my observations are correct. I have seen @plantbrain making this statement, or similar, and I am not sure why he says it.

When I drop my pH correctly to get ~30 ppm in my zero KH tank, a drop checker using a typical 4dKH solution shows very strong yellow color, which the guides interpret as too much/toxic CO2. At 40 ppm it's almost orange. Fish and shrimp are fine, not even breathing hard.

It is very likely that either there is a problem with your measurement of CO2 ppm (pH probe), or with the drop checker. Most likely the dKH in your drop checker is too low, or perhaps you did not use distilled water. Bromothymol in 4 dKH water will not lie about CO2 ppm , and 30 ppm will be green.

 

[GreggZ]

If this is indeed true, then my method here is correct. If it's not true, then estimating the starting CO2 concentration is damn near impossible. And statements like "I have 30 ppm CO2 in this tank" are meaningless.

Yes when people say they have 30 ppm CO2 it's pretty meaningless. Without an expensive CO2 meter it's more of an educated guess than an absolute value.

As to degassing I leave a glass full of water out for a couple of days then start taking the pH reading every six hours or so. Eventually it stabilizes. I have found that provides the most consistent reading for me.

Here's some thoughts I put together and posted somewhere on the ways people can get the CO2 ppm wrong. Read at your risk as you might need to lie down with a cold compress on your forehead if you get all the way through it..............................................................

In my opinion there are many ways to get CO2 wrong. Folks will often list tank parameters and say their CO2 is at 30 ppm . But is it? Best answer is “maybe”. And the notion that we want to have 30 ppm Co2 is way oversimplified. In a high tech, high light high tank more is better. For instance in my tank I drop my pH by 1.4 daily via CO2 injection. The charts/calculators would indicate my CO2 level is about 100 ppm . Is it really? I doubt it.

There are loads of ways to introduce errors into the CO2/dKH equation. Let’s start with measuring dKH. Let’s take an example where someone measures their dKH at 5 and measures their fully degassed pH at 7.6. That would indicate a CO2 concentration of 3.78 which would be reasonable at equilibrium with the atmosphere. So they drop pH to 6.6 and claim they have 30 ppm CO2. The first mistake is that fully degassed water already has some CO2 in it so that actually calculates to 37.8 CO2 ppm ..

But let’s say their measurement is off. 99% of folks use a liquid drop kit to measure dKH. If the true dKH is actually 5.7 CO2 would now calculate to 43.09. If the true dKH is 4.2 then CO2 concentration is 31.75 ppm . Either would be easy to do as we are not measuring dKH down to tenths.

So there’s one variable that can have an effect on how we report CO2 concentration. Next is the methodology of measuring pH. Some folks use test strips or liquid kits that can be off by quite a bit. Using the same example above let’s say that that instead of their degassed being pH at 7.6 it’s really 7.4 and instead of dropping to 6.6 it’s really 6.8. This is extremely easy to do when using liquid test kits and deciphering shades of color. Now CO2 concentration would calculate to 23.85 ppm .

And it’s even true when using calibrated probes. A long time ago I tested 3 different calibrated pen type pH meters against each other. They all gave different readings. It’s best to use a higher quality BNC connected double junction type probe. Much more accurate but still not lab grade equipment.

So the point is many times the reality is that measuring pH drop and dKH are a garbage in garbage out methodology. And when you combine errors in both readings you can begin to see how two people testing the same water could come to wildly different conclusions about their CO2 ppm . So when someone says my CO2 is at 30 ppm , most times they really have no idea if that is true or not.

Then you can also bring in other variables which can affect pH. Our tank is not a lab. There are many other forces at play. Source water dKH can change over time, even seasonally in many places. Some municipalities inject things like Sodium Hydroxide to alter pH. And many factors can affect CO2 concentration in the tank. As plant mass changes so does CO2 consumption (anyone ever notice how a tank perks up when you massively trim a jungle?). Changes in surface agitation/aeration can affect CO2 levels. CO2 diffusers can clog and become less efficient. The flow rate of pumps/filters can change affecting CO2 dissolution. And the list goes on and on.

So then the question is why does it matter? In my experience optimizing CO2 makes every single other thing easier. If you get CO2 right, you have much more leeway as to nutrient dosing, as a wider range will still produce very good results. Folks love to discuss dosing down to the smallest detail. This ratio vs that ratio. Lean vs rich. And the list goes on and on. In my experience if you take the time to get CO2 right, these topics become far less important.

So if we can’t trust the CO2 ppm calculation, how do we dial in CO2? First is having a reliably constant flow rate of CO2. Many cheap needle valves drift. Counting bubbles accurately is all but impossible and bubbles are not a uniform measurement. I use a flow meter and even that can have limitations. So the odds of someone’s CO2 ppm being constant is low.

For me the best method is trial and error and patience. Closely observe both fish and plants while dialing in CO2 slowly over a period of time. Plants will provide subtle clues as you get closer to your optimum concentration. If fish show distress time to back it off just slightly. And one thing many don’t consider is that O2 and CO2 are not mutually exclusive. That is you can have and want high levels of each. If you have good surface agitation (O2) you can have higher levels of CO2 without affecting livestock.

I can tell you this. If I see something wonky in my tank, the first thing I do is check and double check CO2 levels. If it’s off I could waste a lot time playing whack-a-mole with ferts or other things when the real issue is something completely different.

 

[Yugang]

Yes when people say they have 30 ppm CO2 it's pretty meaningless. Without an expensive CO2 meter it's more of an educated guess than an absolute value.

Reality is that even expensive CO2 meters need calibration, and result depends on measurement procedure. I spent some time to study their technology, which is beyond the scope of this thread. They have a digital CO2 ppm display, but this does not necessarily mean they are right or accurate. If we believe their results are accurate, how would we experimentally confirm that?

Is it really? I doubt it.

Respectfully @GreggZ this is because you don't apply chart/calculators correctly, as per below...

There are loads of ways to introduce errors into the CO2/dKH equation. Let’s start with measuring dKH. Let’s take an example where someone measures their dKH at 5 and measures their fully degassed pH at 7.6. That would indicate a CO2 concentration of 3.78 which would be reasonable at equilibrium with the atmosphere. So they drop pH to 6.6 and claim they have 30 ppm CO2. The first mistake is that fully degassed water already has some CO2 in it so that actually calculates to 37.8 CO2 ppm ..

Assuming that degassed water has something like 3 ppm CO2 is a popular assumption in the hobby, but it is wrong. And this matters a lot, because we use this reference for an exponential/logarithmic extrapolation which will blow up any error. I had same discussion with @Dennis Wong , and after refining his method of outgassing also confirmed with his professional CO2 meter that in reality it is about 0.6 ppm . Many hobbyists, including very experienced, don't outgas properly, and are not familiar with Henry's law of partial pressures.

For instance in my tank I drop my pH by 1.4 daily via CO2 injection. The charts/calculators would indicate my CO2 level is about 100 ppm . Is it really? I doubt it

I also doubt it. If you would take a 1.4 drop starting with the 0.6 equilibrium with outdoor air, rather than 3 you will find a more reasonable number than 100 ppm .

If the true dKH is actually 5.7 CO2 would now calculate to 43.09. If the true dKH is 4.2 then CO2 concentration is 31.75 ppm . Either would be easy to do as we are not measuring dKH down to tenths.

I usually measure KH by multiplying the aquarium water volume by 4, then divide the number of test drops by 4 as well to have approximately 0.25 resolution if KH measurement. An error of 5.7-4.2 = 1.5 is unlikely. An 0.25 resolution translates into acceptable errors for CO2 ppm calculation.

A long time ago I tested 3 different calibrated pen type pH meters against each other. They all gave different readings. It’s best to use a higher quality BNC connected double junction type probe.

Definitely, don't use a cheap pen. As you say garbage in garbage out.

So the point is many times the reality is that measuring pH drop and dKH are a garbage in garbage out methodology. And when you combine errors in both readings you can begin to see how two people testing the same water could come to wildly different conclusions about their CO2 ppm . So when someone says my CO2 is at 30 ppm , most times they really have no idea if that is true or not.

Fully agree. The point is that every method of measuring CO2 in water has its pitfalls. All (currently commercially available) CO2 measurement methods in water suffer from the slow CO2 diffusion from the water into whatever does the measurement, and will benefit from flow and turbulence. I would argue that when done well, pH drop is one of the most reliable, and I double check with drop checker that takes out the chemistry from the equation. Also professional dissolved CO2 meters need calibration and proper, lengthy, measurement procedures. CO2 meters are good and fast at high CO2 ppm 's, but they struggle with low CO2 ppm 's as also their scientists have published.

So if we can’t trust the CO2 ppm calculation, how do we dial in CO2? First is having a reliably constant flow rate of CO2. Many cheap needle valves drift. Counting bubbles accurately is all but impossible and bubbles are not a uniform measurement. I use a flow meter and even that can have limitations. So the odds of someone’s CO2 ppm being constant is low.

Unless we have a method that by the laws of physics stabilises CO2 injection into the tank's water. It's there, it just needs a bit more time to be discovered by the hobby.

I can tell you this. If I see something wonky in my tank, the first thing I do is check and double check CO2 levels.

How do you double check? Probably still pH probe?.

I believe that the key take away from your post is that we should not have tunnel vision on CO2 ppm 's, and should focus on CO2 stability, plant health and fish health?

 

[GreggZ]

I believe that the key take away from your post is that we should not have tunnel vision on CO2 ppm 's, and should focus on CO2 stability, plant health and fish health?

Your post is an excellent example of why we don't really know the absolute CO2 ppm in our tanks.

But I should have added that it really doesn't matter and we really shouldn't care. Like you said, we should focus on CO2 stability, plant health, and fish health.

The thing we can control is the relative pH drop. So for instance in my tank a 1.2 to 1.4 pH drop is a good balance between plant health and fish health. Whether my initial assumptions/readings/calculations are wrong doesn't matter. I just know that with whatever flawed information I am using if I keep it in that sweet spot the tank does better. Knowing the actual CO2 ppm is meaningless so focus on what you can control.

 

[Burr740]

This is a very interesting topic and Im pretty sure we've all been doing it wrong. I dont think my degassed values are exactly right so my drop of 1.2 is probably a lot more. Ive always know we're not accurately predicting the ppm . What I do know is a certain level is needed, and going much higher brings negative returns, as well as lower obviously. But this is extremely interesting and I freakin love it when new discoveries comes along that clear up something thats been long misunderstood

I have a question. Is the baseline of .6 ppm from truly degassed water, or after its reached equilibrium with the atmosphere again?

 

[Yugang]

I have a question. Is the baseline of .6 ppm from truly degassed water, or after its reached equilibrium with the atmosphere again?

This is really a good catch - it is in equilibrium with atmosphere, and indeed not fully degassed. With 'atmosphere' we mean the 400 ppm CO2 outdoor, and as mentioned before be careful with indoor air that could easily be 1000 ppm or more.

 

[Anonymous_One]

In my opinion there are many ways to get CO2 wrong. ... In a high tech, high light high tank more is better. For instance in my tank I drop my pH by 1.4 daily via CO2 injection. The charts/calculators would indicate my CO2 level is about 100 ppm . ... In my experience optimizing CO2 makes every single other thing easier. If you get CO2 right, you have much more leeway as to nutrient dosing, as a wider range will still produce very good results. Folks love to discuss dosing down to the smallest detail. This ratio vs that ratio. Lean vs rich. And the list goes on and on. In my experience if you take the time to get CO2 right, these topics become far less important ...

In all seriousness, I'd be interested to know why you think (i.e. on what rational grounds you have come to the conclusion) that a high or stable CO2 concentration (30+ ppm ) is what matters most in planted aquariums. Why do you think this (= high and stable CO2 concentration) is more important than that (= balanced nutritional diet)?

Surely you know the graph of growth rate vs nutrient concentration:



If you plug in CO2, you get that even though plants will reach their maximum growth rate at, say, 26 ppm , they will reach half (50%) of their growth rate at as low a concentration as 4 ppm , and at ~10 ppm they will reach 90% of their growth rate.

So I ask: Why do you think it's so important to have 30 ppm CO2 (or even more) in your aquarium and that this concentration should not fluctuate? According to some objective natural law expressed by the graph, this is nonsense. Even just 4 ppm CO2 will ensure that my plants grow perfectly well. So why would it be so important to push it to that extreme (and, according to the law of diminishing returns, highly inefficient) 30 ppm ?

PS: My point is not to dispute that higher CO2 concentrations may be a better solution in certain cases, but rather to get others to use rational reasons to defend this view, rather than just repeating various dogmas. Indeed, just plug into the equation the results achieved by Sudipta Shaw with his "non-CO2 supplemented tanks" and your idea of the need for high/stable CO2 concentrations gets seriously cracked.

 

[Burr740]

@Marcel G the references to "growth rates" assume plants can grow and stay healthy at those lower rates. The rate of growth refers to speed. Health is assumed and its a big assumption

Take for example the claim of 50% growth rate with only 4 ppm of, lets say NO3 (graph just says "nutrients", its certainly not the same for each one) That assumes 4 ppm is enough to grow plants healthy while we observe their rate of growth. There's a sweet spot for growing plants healthy too, and 4 ppm of no3 is not gonna cut it for most plants in a co2 injected high light tank. Unless of course its set up to run low no3 with fresh rich substrate, but thats beside the point here, which is the graph has problems

 

[Anonymous_One]

I would say that my assumption (regarding healthy plant growth even with significantly lower CO2 concentration than you normally use and recommend) is definitely more justified than your assumption that "high or stable CO2 concentration is what matters most in planted aquariums". Please see this post and that subsequent one. I would say that the vast majority of tropical plants grow in waters where CO2 concentrations do not exceed 10 ppm . In post #5 I even list a range of values for K1/2 (which is just that 50% photosynthesis/growth rate), and as you can see, for "strict CO2 users" it is somewhere around 5 ppm (which is really close to what I originally "pitched"). Do you really think that plants can only grow well at high nutrient concentrations (including CO2)? Doesn't nature prove us otherwise today and every day? Aren't most natural waters oligotrophic (i.e. very low in nutrients)? Yes, most plants root in mud (= nutritient rich substrate), but they don't have much nutrients in the water. It's just that you are advocating high nutrient concentrations in the water column => 30+ ppm CO2 in the water (not in the substrate). And that's what I was objecting to. How many tropical rivers do you think have NO3 concentrations above 4 ppm ? For example, in the book "Aquarium Plants" (2020, Christel Kasselmann) the author states that the average NO3 concentration in Amazonian "black water" is around 1.6 ppm , in "clear water" 0-0.08 ppm and in "white water" 0.8 ppm (ammonium is mostly unmeasurable or below 0.2 ppm there) - see p. 595. Yet you want to tell me that most of the plants there in those rivers are languishing and look "about to die"? Of course in natural waters plants grow under direct sunlight (1500-2000 PAR, underwater in most places about 300-1000 PAR). So I don't really understand your explanation.

 

[GreggZ]

In all seriousness, I'd be interested to know why you think (i.e. on what rational grounds you have come to the conclusion) that a high or stable CO2 concentration (30+ ppm ) is what matters most in planted aquariums. Why do you think this (= high and stable CO2 concentration) is more important than that (= balanced nutritional diet)?

I should have clarified that my comments are based on a high tech high light tank full of stems and mostly fast growing plant species. I am not really interested in how that correlates to plants growing in a stream or lake, as our aquariums have very little in common with what happens in nature.

And my comments don’t come from charts, graphs, or scientific studies. They are a result of observing high tech high light tanks for many, many years. Both my own and hundreds of other people’s.

And in my experience, getting CO2 right does make everything easier. It’s been shown by loads of people for many, many years. Take a high tech tank that is humming along and deny it CO2 and be prepared for all types of trouble to break out.

Now as to stability my belief is that plants do not like change. Think of a factory that is humming along making widgets. Everything is running like clockwork. Then disrupt the supply chain and all heck can ensue. Once plants get “programmed” to make the best use of what you are supplying, when you change that plants reprogram themselves which can wreak some havoc while they adjust.

As to nutrition I think people spend way too much time focusing on it. It blinds them to everything else that makes a planted tank healthy. They get so caught up with nutrient tunnel vision that they can’t see the forest through the trees. In my tank (and many others that I know very well) if CO2, maintenance, light, horticulture, flow, temperature, etc, etc are in good ranges you can get by pretty well with a fairly wide range of nutrients.

And this is in no way to say that this is the only method that works. I’ve been around a long time and have seen tanks do very well under vastly different methodologies. Sudipta’s is a great example. It’s a bit of an outlier but you can’t deny his results. But to repeat his results you need to dig deep and understanding everything he is doing.

In fact when I first ran across Sudipta I was having conversations with Tom Barr and some others about his results and they insisted he must be using CO2. I stuck up for him and it took some time but eventually people came around and saw that he wasn’t and that he had created something pretty unique. But if you get to know Sudipta you realize it hasn’t all been roses. He runs across issues just like anybody else and the tank needs to be kept within certain parameters or he runs into problems too. And there are a few people who have repeated his results but not many in the scheme of things.

In the end there are lots of ways to manage a planted tank. If you can show me a colorful healthy display then I am interested to learn more. There is no one right or wrong way. That being said I know many of what I consider to be some of the best planted tankers in the world. They have lot’s of things in common (for instance good CO2), but fertilizer dosage is usually not one of them.

 

[Yugang]

We may be conflating several conflicting perspectives and objectives above. Natural habitats versus scaped tank. Focus on 'hard' species or more mainstream easier plants. Commercial plant farming. Objectives on growth rate and maintenance. Livestock health. Cost of equipment and CO2 consumption. To mention a few.

Several of the most experienced scapers, including @GreggZ , state that CO2 is always the first to check if anything is wrong with the plants. @plantbrain usually states that 90% of problems in high tech tanks are CO2 related - a statement that is based on hundreds of tanks and virtually never challenged by anyone with experience.

There seems to be some mysticism regarding what "good CO2" means. I asked several opinion leaders and never got an entirely clear answer, or at least so that I could understand it. I am mostly interested what "stability" means. Are we interested in stability within the day's photoperiod (as most hobbyists seems to assume), or rather averaged over longer periods like days and weeks (this is my personal belief). The other part of "good" CO2 is the absolute level, where it is usually assumed that more is better and we want to go as far as the fish can tolerate. And then not to forget water flow, so that CO2 is nicely distributed in the tank and plants have easier access as we avoid to some extent the limitations of diffusion.

I have been fascinated for years why we target high CO2 ppm rates, and almost all advice to newbies is to use the standard 4 dKH drop checker and do 30 ppm CO2. Is it simply because the easiest is to follow the pioneers in high tech tanking, as well as the best contemporary scapers? Are there objective arguments that higher CO2 levels work better?

So here is my question, as pointed as I can:

Is it possible to create an award winning Dutch tank, when limiting CO2 to 10-15 ppm (green on 2 dKH drop checker). Besides the obvious disadvantage that preparation of the winning scape will be more time consuming, what are the other challenges and how can they be overcome?

 

[Anonymous_One]

I should have clarified that my comments are based on a high tech high light tank full of stems and mostly fast growing plant species. I am not really interested in how that correlates to plants growing in a stream or lake, as our aquariums have very little in common with what happens in nature. And my comments don’t come from charts, graphs, or scientific studies. They are a result of observing high tech high light tanks for many, many years. Both my own and hundreds of other people’s ...

From your answer, I guess there is no point in further discussion. Nevertheless, I will not forgive myself for a small remark: Either the laws of nature are valid, or they are not laws of nature. So, if one can figure out that plant growth is related to nutrient levels in a non-linear way, then a number of instructive conclusions follow (regardless of whether the plants are growing in nature, in a garden, or in an aquarium). The fact that you don't have the will to learn from these laws is, of course, your business. But I think it is very damaging to aquaristics when you promote your pseudo-scientific views (i.e. views that question the validity of the laws of nature) among other aquarists. And to take the consensus of aquarists as proof of the truth of their views is perhaps not even worth commenting on. In the Middle Ages, for example, the consensus was that the center of the universe was the Earth. We all know how "true" that consensus turned out to be. I would rather not comment any further, or I'll be excommunicated again. I also apologize for disrupting the original topic.

 

[plantbrain]

Is it possible to create an award winning Dutch tank, when limiting CO2 to 10-15 ppm (green on 2 dKH drop checker). Besides the obvious disadvantage that preparation of the winning scape will be more time consuming, what are the other challenges and how can they be overcome?

Perhaps, but ponder this: pre 1980's, there were intense debates over the usage of CO2 for the NBAT contest. The 2 sides argued quite intensely. But..........there were planted tank winners that did not use the CO2. Non CO2 planted tanks, and.....they looked quite nice. Now this is LESS than 10-15 ppm .

Also note, that Light was much lower, a single or pair, of T12 lights. You might get 30-40 umols of light. The low end. ADA's scam as I've called it for a long time was they made these 1st generations light to match 40-50 umol of light, I measured 6 ADA tanks(An ADA Japan trained importer and Dealer) and from that Data, you can estimate many of the tanks in showroom in Japan. You know the light, you can see the distance above the tanks. So you can come pretty close to the intensity. They often used 10 hours light cycles. Their data makes no sense for KH and pH vs the CO2 ppm they state in the books. Still, at low light, even the HQI metal halide bulbs..........had the same umols in every......single tank. Most of the planted tanks in the NBAT had T12 and then later, T8's, did not see any T5's really. 30-50 umol range was typical.

Low light, less CO2 demand for the plants. In fact, you can grow plants well with light so low, in a non CO2 enriched system, the plants would die from a lack of light. Adding the CO2 means less CO2 uptake enzymes(rubsico) are needed so more can be diverted to light gathering. It makes a far more robust method for newer hobbyists and beginners, as well as seasoned vets that want less work. 10 vs 15 ppm is a pretty large difference compared to say 40-45 ppm . I think in many such cases as well as ADA's data, we can see cases where there is ample potential for the ppm 's to be off.
Same for NO3/PO4 measurements. Over time, many adjust the gas upwards if they have a well run tank or already started there and left it.

So there's several things going on with data and hobbyists. Few use a reference. Too much work for some. Some just do not care as long as things look and grow good. My tanks where I did use a 2 part reference ended up being much higher than I thought. 55, 45 and then 70 ppm for a 70, 120, and then the 180. These ran clean for for a decade. The 180 gallon with the 70 ppm CO2 never had any algae. I added algae covered plants, all sorts of replacement and additions of algae. Nothing took root. Plant health was phenomenal. the 120 with the 45 ppm was the most testy and got a tingle of different algae species here and there. It had higher light as well, not much more than the 180. I got curious so I lowered the lights on the 180 to match the umols. No effect really.

So is there an immediate range? 10-15 ppm ? Yes!
Do you put 100-200 umol of light on such a tank? Hell no.
Do you use 40-50 umol, sure with the caveat that you will adjust the CO2 upward as needed rather than force everything with sticking with this dissolved the gas range of 10-15 ppm .

Potential short comings: Liebig's law. If you moderate to strongly limit a nutrient for the plants, more than the CO2 demand, then that will control the plant growth, and PO4 stress is a lot better than CO2 stress for most plant species. Same deal with N, K, etc. We like to assume independence but low ppm of ferts can dramatically impact small limitations for CO2. PMDD is a classic example. Add the CO2 ppm higher, then you can add more/lots of PO4. If CO2 ppm is low, then limiting nutrients will have a strong effect. Same with limiting light. Light limitation s likely the wisest approach, then look at CO2, then........look at ferts at the end of all this downstream growth factors.

There are other things also, % and frequency of Water changes, temperature(warmer is going to rougher and faster for growth, low temps, easier). "Arms in the tank", sanitation, cleaning, general consistent routines.

If your CO2 gas tank runs out and you are me or the NBAT contest entrants? We both get hair algae. We add the CO2 back? It stops and slowly goes away, Cladophora, and the softer species of green hair algae(there's 4-5 other genera that are common).

I do not think aquarist should piece meal the variables, they are interrelated and dependent on eachother in a flow from where photosynthesis starts. If you have enough control to make the other variables independent..................they you can do good test methods because you have control. Those lacking this control(Algae and those with issues or plant growth issues)? They cannot.

Long winded answer. Highest % chance at high success? Low light in that 30-40 umol range(LED preference since easy to adjust intensity and colors to suit), ADA AS, lower light EASY species, lower temps, 20C etc, frequent water changes(this mitigates the low CO2 potential issues), Good pruning skills, clean filter monthly, keep glass clean, decor etc.

 

[plantbrain]

I should have clarified that my comments are based on a high tech high light tank full of stems and mostly fast growing plant species. I am not really interested in how that correlates to plants growing in a stream or lake, as our aquariums have very little in common with what happens in nature.

And my comments don’t come from charts, graphs, or scientific studies. They are a result of observing high tech high light tanks for many, many years. Both my own and hundreds of other people’s.

And in my experience, getting CO2 right does make everything easier. It’s been shown by loads of people for many, many years. Take a high tech tank that is humming along and deny it CO2 and be prepared for all types of trouble to break out.

Now as to stability my belief is that plants do not like change. Think of a factory that is humming along making widgets. Everything is running like clockwork. Then disrupt the supply chain and all heck can ensue. Once plants get “programmed” to make the best use of what you are supplying, when you change that plants reprogram themselves which can wreak some havoc while they adjust.

As to nutrition I think people spend way too much time focusing on it. It blinds them to everything else that makes a planted tank healthy. They get so caught up with nutrient tunnel vision that they can’t see the forest through the trees. In my tank (and many others that I know very well) if CO2, maintenance, light, horticulture, flow, temperature, etc, etc are in good ranges you can get by pretty well with a fairly wide range of nutrients.

And this is in no way to say that this is the only method that works. I’ve been around a long time and have seen tanks do very well under vastly different methodologies. Sudipta’s is a great example. It’s a bit of an outlier but you can’t deny his results. But to repeat his results you need to dig deep and understanding everything he is doing.

In fact when I first ran across Sudipta I was having conversations with Tom Barr and some others about his results and they insisted he must be using CO2. I stuck up for him and it took some time but eventually people came around and saw that he wasn’t and that he had created something pretty unique. But if you get to know Sudipta you realize it hasn’t all been roses. He runs across issues just like anybody else and the tank needs to be kept within certain parameters or he runs into problems too. And there are a few people who have repeated his results but not many in the scheme of things.

In the end there are lots of ways to manage a planted tank. If you can show me a colorful healthy display then I am interested to learn more. There is no one right or wrong way. That being said I know many of what I consider to be some of the best planted tankers in the world. They have lot’s of things in common (for instance good CO2), but fertilizer dosage is usually not one of them.

Here's a generalized graph, I have dozens of others. Note, the axis can be replaced with other things like PPM in the Water(X axis), or relative growth rate or O2 ppm evolution from the plants etc for the Y. It's non linear. I dod not like to add ppms or units on these graphs for good reason: they are general concepts, not specific to an aquarium, there are many other factors that increase or decrease the rates of growth and light/CO2/ppms/water changes/flow etc are just some of those.

Note, I grew the Ammania pedicillata as well in non CO2 tanks. It look so so but still grew.
It looks really pretty in a CO2 enriched ADA soil tank without any added ferts, just a couple of algae sticks for the shrimp once every week or so.
In fact, it looks better than anyone's tank I've seen to date. Same for the A. gracilius 'crassicalius' red variety. I think LED lights have helped to a large degree, clay soils. Certainly easier to replicate. Still, I would say those tanks get less water changes than most any CO2 enriched tanks and less care. Labor wise, they are easily on par with most any non CO2 tank. We can skin this cat a few ways, pick your poison. Now suppose the Sudipta tank was a 20" deep larger tank, this is something he might try at some point to see it scales up nicely, or not.