Question of the Day Ideal fertilizer ratio for aquarium plants?

[Art]

Hi ScapeCrunch family! I hope you're having a wonderful weekend.

It's been said that most aquatic plants are usually around 7-1-8 (N-P-K) by mass. Why then are we not targeting this with our fertilizer regime?

I do realize that every plant may have a different requirement, like most of us as humans. However, we do all take a daily vitamin pill that must have a standard formula for all of us. Perhaps it hits the average requirement and that's what we should target?

Think about it, if we agreed that the above ratio works and should be the standard, then things become easier. Just tie everything to it and you just need to test N to make sure you're at 7 and everything else should be good. Right?

I also understand that over time you will see what works with your particular aquarium and you can tweak it to improve your situation over time. I get that. However, my question goes to the starting point for hobbyists before they learn what their aquariums prefer.

Would really appreciate your thoughts here. If you're a newcomer, wouldn't this be easier for you? What are you doing today?

If you're a more seasoned hobbyist, you're rolling your own, probably. Tell me what you think about this as a starting point. How did you arrive at your starting point?

 

[BigWave]

You know, back when I 1st got into planted tanks mostly on forums because social media wasn't around then, ratio's and targets were all everyone talked about. For about 3 years I was obsessed with figuring out the correct N:K or even P to Fe ratio's (Think Mulders Chart, Antagonism vs Synergism). I even tried making a calculator by plugging in all these so called ratio's. Wasn't technically inclined back then so it didn't work out well. The point is, once I let all this go and just started dosing as per recommendations on the bottle my plants started to do better and actually grow properly. Now looking back its just like Tom Barr has said all along. Aquatic plants don't care what ratio of elements are in the water coloum, they take what they need.

 

[EDGE]

this topic has been conflated over the years and given the casual hobbyist now a days uses substrate, which in itself is formulated with a ratio, there is less talk about dry bulk dosing vs commercially available premixed ratio dosing fertilizer.

There is 2 part to the "ratio" topic.
1 is dosing by ratio, which is what we all do
2 is maintaining a ratio

Plants do care the ratio of the nutrients, but we in some regard ignore this by the weekly water change to reset the tank. This mostly negate the 2nd part.
Add to the equation is ADA like substrate vs gravel (cation exchange capcity and very little CEC )
The plant type - stem plants vs bulbous, rhizome, tuber plant in a tank.
The fish load

The starting point for someone new to the hobby at this stage of the hobby is follow the full line of the product from a company or kind of get left questioning if they are doing something wrong.

That being said, what they need is to find information pertaining to gravel tank vs substrate tank; Understand how CEC work. When the phosphate is depleted in the substrate after the first 2 year of use, PO4 deficiency symptoms is not far behind.

Next they should have some information on requirement of different plant type (i.e. stem, rhizome, bulbous, tuber etc) not specific to species - a rhizome plant like a crypt and a rhizome plant like an anubias requirement are not big of a different. The only different is one has access to fish waste in the substrate and the other doesn't. Stem plant and moss like plant has a higher consumption of nitrate compared to bulbous, rhizome, tuber plant which require a lot more phosphate - which sadly the internet is lacking in information.

Finally, offset the amount of ammonium from the fish load and the binding properties of CEC for cation, i.e. ammonium, calcium, magnesium and potassium.

In a good case scenario, for people that don't do 50% water change weekly, the TDS should fall over the week from once a week dosing or remain relatively stable if fertilizer is being added regularly.

Just do 50% weekly water change and ignore everything above

 

[GreggZ]

There is 2 part to the "ratio" topic.
1 is dosing by ratio, which is what we all do
2 is maintaining a ratio

Plants do care the ratio of the nutrients, but we in some regard ignore this by the weekly water change to reset the tank. This mostly negate the 2nd part.

Can you elaborate on this? How does weekly water change negate the ratio? I am guessing you mean removing nutrients so the tank is leaner after a water change?

If so this is not necessarily true. Many in the hobby perform very large water changes but go to great lengths to keep the water column numbers stable.

Hi ScapeCrunch family! I hope you're having a wonderful weekend.

It's been said that most aquatic plants are usually around 7-1-8 (N-P-K) by mass. Why then are we not targeting this with our fertilizer regime?

In my opinion the idea that we need to dose according to analysis of plant mass is wrong. We want to dose levels that bring out the best in plants.

Truth is I have seen all kinds of people successful at many different ratios. If you get everything else right you have a lot of leeway. That being said if you get to know many of the best plant growers in the hobby you begin to see a lot of similarities. Take Dennis Wong and APT Complete. Roughly 2.5 : 1 : 5.5 ratio. Works for a lot of people with medium energy tanks. Most that I know with higher light higher energy tanks dose a bit more NO3 and PO4 more like 4 : 1 : 5. But again, there is no magic ratio, and as long you have enough but not too much of each plants will do fine.

And the truth is most of the liquids out there will be fine for most of the people. People who are new to the hobby blame everything on fertilizers, but the reality is most of their problems are not fert related.........unless they are dosing way too little.

 

[Art]

Thanks, guys. I started this thread to flesh out a concept that was talked about at length in the past. I remember many conversations about toxicity, antagonism and needed ratios. It's interesting to understand what everyone is thinking today.

I do think that a plant species may have a ratio preference among some of the nutrients. And, I know from scientific studies, that nutrient antagonism is real. Nutrient antagonism refers to chemical reactions that interfere with overall plant development and growth. However, in practice, I've rarely run into an issue with this and I think the same is for most out there.

My concept is, if I put 10 ppm of nitrate and 10 ppm of potassium into the water column, the plant will take the ratio of nitrate and potassium that it needs and leave the rest in the water column. We are not force feeding plants. They eat what they want and leave the rest.

Then, the weekly water change ensures that the "rest" that wasn't taken up, does over accumulate in the water column over time. Simple concept.

If you think the above is true, then why do fertilizers like APT or even our DIY formulas worry about ratios?

 

[BigWave]

I know in some of my past tanks if I missed a few weeks of water changes say 2 yet kept dosing as normal, you could physically see the rapid decline in growth / luster / color etc of the plants. Its as if someone flipped a switch. I attribute this to excess of something in the water coloumn.

 

[EDGE]

How do we quote on here with link to the post?

My concept is, if I put 10 ppm of nitrate and 10 ppm of potassium into the water column, the plant will take the ratio of nitrate and potassium that it needs and leave the rest in the water column. We are not force feeding plants. They eat what they want and leave the rest.

Then, the weekly water change ensures that the "rest" that wasn't taken up, does over accumulate in the water column over time. Simple concept.

If you think the above is true, then why do fertilizers like APT or even our DIY formulas worry about ratios?

I think the ratio is to reduce the speed of excess accumulate over the week when one does not test regularly. Certain ratio is adjusted to work with particular substrate. If I remember correctly, APT complete is based off of finding the middle ground with the ADA system and EI.

Take for example

Assume the plant use 10 nitrate 5 potassium.

We add 10 nitrate and 10 potassium.
after 2 days tank is at 0 nitrate and 5 potassium in the water.
We add 10 nitrate and 10 potassium without testing based on a predetermined dosing regime - tank is at 10 nitrate and 15 potassium.
after 2 days tank is at 0 nitrate 10 potassium
We Add 10 nitrate 10 potassium. - tank is at 10 nitrate 20 potassium.

But if we were to dose 10 nitrate and 8 potassium
on the 5th day we are at 10 nitrate 14 potassium rather than 10 nitrate 20 potassium.

Honestly, the different between adding 10 NO3 and 10 K vs 20 NO3 and 20 K at a time is how fast the plant grow and how fast the tank end up with excess.

If so this is not necessarily true. Many in the hobby perform very large water changes but go to great lengths to keep the water column numbers stable.

When people test to see if the tank is stable, are they testing to see if they have detectable range of NO3, PO4 and K in the water testing to see if they are within a "range"? What is stable in this context?

If we monitor the tank for stability, like an aquaponic system which doesn't get large amount of water change, what is the reason we still do water change?

deficiency symptoms of plants can also be caused by the excess of element. There is the hidden Sulphate which we don't test that will accumulate overtime - which Bigwave mentioned when he didn't do water change for a few weeks.

There are many that doesn't test regularly and rely on water change to reset the parameter. Isn't this is what EI is based around?

Is there a new range for the different element now? I look at APC and the target range is quite huge.

10-30 ppm of NO3
1-2 ppm of PO4
10-30 ppm of K
30 NO3 to 1 PO4 to 30 K is asking for trouble with root growth and leaf deterioration which lead to algae.

If you look at a different approach
10-1-13 is quite huge. This probably assume there is a lot of fishwaste accumulated over the years to offset the low PO4 and the fish ammonium production is less than the solids they give.

The is information from 15 year ago should be change to reflect on newly accumulated knowledge.

Truth is I have seen all kinds of people successful at many different ratios. If you get everything else right you have a lot of leeway. That being said if you get to know many of the best plant growers in the hobby you begin to see a lot of similarities. Take Dennis Wong and APT Complete. Roughly 2.5 : 1 : 3 ratio. Works for a lot of people with medium energy tanks. Most that I know with higher light higher energy tanks dose a bit more NO3 and PO4 more like 4 : 1 : 5. But again, there is no magic ratio, and as long you have enough but not too much of each plants will do fine.

I thought APT Complete has higher potassium? 2.5-1-5.5?

Good thing is, APT FAQ uses NO3, PO4, and K
On a somewhat different topic. There is a conversion factor at play for people new to the hobby. People look at a commercially sold bottle of fertilizer, a lot of times, the ratio are based on N, P2O5 and K2O. In this hobby, most of us talk using NO3, PO4, and K
In some research people online uses N - nitrogen, P - phosphorus, K - potassium; not nitrate, phosphorus pentoxide, phosphate, Potassium oxide, etc.

know in some of my past tanks if I missed a few weeks of water changes say 2 yet kept dosing as normal, you could physically see the rapid decline in growth / luster / color etc of the plants. Its as if someone flipped a switch. I attribute this to excess of something in the water coloumn.

Is there something different you do now you can get away without doing water change for a few weeks and not have issue with plant growth?
What did you dose with before and what do you dose with now?

I tied my Calcium and Magnesium dosing as a % of Potassium and not based on starting at 3+ gH

Ca = 40 to 60% of Potassium ppm
Mg = 9.5 to 13% of Potassium ppm

 

[GreggZ]

I know in some of my past tanks if I missed a few weeks of water changes say 2 yet kept dosing as normal, you could physically see the rapid decline in growth / luster / color etc of the plants. Its as if someone flipped a switch. I attribute this to excess of something in the water coloumn.

Steve when you say you attribute it to an excess of something in the water column, have you considered that it might not be excess nutrients, but rather dissolved organics in the system?

And then the next question would be how much of what were you dosing? And if you suspect it's nutrients then what level of which nutrient would you suspect? Did you do any testing of nutrients levels to see what was going on?

Did you ever try maintaining the water change schedule but increasing ferts to those levels to see if you could induce the symptoms removing water changes from the equation?

Lastly would be what type of tank was this? High light/stems? Lower light slower growers?

 

[GreggZ]

When people test to see if the tank is stable, are they testing to see if they have detectable range of NO3, PO4 and K in the water testing to see if they are within a "range"? What is stable in this context?

I can offer what I observe in my own tank. My dosing is designed to keep stable levels of nutrients in the water column. I can test any day of the week and those levels are almost exactly the same. If I test right before and after a water change the levels are almost exactly the same. In fact my TDS is almost exactly the same before and after a water change. In this context I would call my nutrient levels in the water column very stable.

deficiency symptoms of plants can also be caused by the excess of element. There is the hidden Sulphate which we don't test that will accumulate overtime - which Bigwave mentioned when he didn't do water change for a few weeks.

In my opinion you would need a wildly high amount of sulphate to see any negative effects. It's just something folks should not really be worried about. There a dozen things that are more important to the health of a planted tank. In my opinion I have seen far more problems with plants/algae as the result of under dosing, not over dosing. Weak starving plants are a magnet for algae.

Is there a new range for the different element now? I look at APC and the target range is quite huge.

10-30 ppm of NO3
1-2 ppm of PO4
10-30 ppm of K
30 NO3 to 1 PO4 to 30 K is asking for trouble with root growth and leaf deterioration which lead to algae.

Whose is suggesting this target range?

I thought APT Complete has higher potassium? 2.5-1-5.5?

You are correct. I had a typo I will go edit.

APT Complete is 7.2 : 2.8 : 15.2

APT EI is 13.8 : 4.5 : 15

 

[LeperKuN]

Liebig's Law of minimum tells me ratios are obsolete for plant growth. I can imagine ratios are good to extend your fertilizer supply. Check how fast this and that is absorbed and adjust accordingly. I'm still learning but that's what I figure.

 

[Art]

How do we quote on here with link to the post?

Good question. Just highlight the section of the post you want to quote and a reply button will pop up. When you post that, it appears with the original poster's name and a link to the post you quoted.