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The mystery of KH and running with zero KH

Art

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  • Oct 29, 2022
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    Miami, FL
    It's been a while but more and more aquarists seem to be running their tanks at zero KH. These tanks are very healthy and beautiful so it seems to at least not hurt the plants and it may be very helpful, especially with some difficult species. As you may know, KH is the presence of carbonate and bicarbonate anions in the water.

    Putting aside the accuracy of our test kits which have a margin of error that may result in a 1, 2 or 3 KH but still read it as zero, let's just agree that these aquarists are running low or no KH.

    The question I have is why does low or no KH result in better growth for some species of plants, particularly stems?

    Also, what role, if any, does pH play in this? Does it matter if someone is at 7 pH versus 5.7 pH?

    Lastly, how does this impact the fish, invertebrates and microorganisms in the aquarium?
     
    While I can't share a lot of the science behind it, a few common "marketing" terms have been tossed around, and they are generally agreed upon.

    Low or no KH will result in a pH ~ 7 or so, add CO2 / humic acids from natural decomposition and you are left with a pH somewhere in the 6's. Nutrient availability and a plants ability to uptake nutrients is best averaged out in the mid 6 - 7 pH range. In terms of fish, I believe it's the ability to regulate osmotic pressures - and most fish prefer softer water (low KH). However with more and more domesticated linage, we are seeing a vastly broadened range where common aquria fish can thrive.

    So to answer your question about a pH of 5.7 vs 7.0, yes it can make a difference - mostly in converting nutrients into plant available forms and keeping them in that window for long enough where plants can uptake them effectively. Just because you dump Iron into your tank, does not mean the plants can actually uptake it for it example. pH also dictates which chelates are more effective:

    "EDTA strongly holds iron in solution up to pH 6.0, but by pH 6.5, almost one-half the iron is precipitated, and by pH 7.0, almost none of the iron is available to plants. DTPA is an excellent iron source up to media pH 7.0; however, 60 percent of the iron is precipitated and unavailable by pH 8.0"

    Running low or no KH does pose a risk, but the pH crash typically talked about is usually caused by a tank full of decaying organics - so rapid that having a low / no KH will result in a pH that drops dramatically - thus a "crash" - I have never once personally experienced this or know of anyone who has.

    So, to be successful having little to no KH, just perform regular water changes and keep up with removing organics (gravel vac / filter cleanout / removal of dead or decaying plant matter).
     
    First of all agree with everything that Quag said above.

    When I decided to go to pure RO and no carbonates added I really didn't know of anybody who was doing it. At the time I was raising my water to 2 dKH via K2CO3 dosing. The issue I had was that I like to use a pH controller. But the soil was fighting my carbonate dosing so pH would not remain stable. I figured rather than fight it why not just see what happens if I don't add any carbonates at all.

    What happened was that the tank was better than ever, particularly with a few known soft water loving plants. And that's not to say you can't have a fantastic tank with moderate dKH. But as dKH rises, the number of species that will get to peak health goes down. So you just need to be more selective about the species you choose. And while there a few species that prefer higher dKH, in general most plants prefer very soft water.

    My fully degassed RO is rock steady at 6.25. I've tested it many times and it's always the same. I drop to 4.85 via CO2 injection daily. My tank full of Rainbowfish are as healthy and colorful as ever. I have a few snails here and there but not many. I doubt my environment is the best for them.

    As to tank biology, it's a myth that nitrifying bacteria can't survive in zero or low dKH water. If you take a look around the world there are many places with naturally soft water. And many people in those areas use an active soil that further drops to dKH to basically nothing. Just saying it's the norm in some parts of the world.

    But still there are old myths that die hard. When I went to zero dKH some people gasped. They have read that such a tank is going to experience a pH crash. In a well maintained aquarium this is nothing to worry about. pH crashes are almost always related to terrible maintenance, lots of dead/decaying plant matter, fish waste, lack of water changes, etc. Basically it's filthy tanks that crash.
     
    Thanks guys. This was bit of a technical question but it's out there and people are seeing it and really don't understand it.

    A few take aways:
    • There are many soft water plants that naturally live in a low KH environment.
    • Running a low KH tank doesn't mean you're walking the razor with a pH crazy at any moment.
    • Even what most would consider an extremely low pH (4.85) is OK with a planted tank and the right fauna.
    Would you guys recommend to a newbie to go zero KH?
     
    Thanks guys. This was bit of a technical question but it's out there and people are seeing it and really don't understand it.

    A few take aways:
    • There are many soft water plants that naturally live in a low KH environment.
    • Running a low KH tank doesn't mean you're walking the razor with a pH crazy at any moment.
    • Even what most would consider an extremely low pH (4.85) is OK with a planted tank and the right fauna.
    Would you guys recommend to a newbie to go zero KH?
    It depends on their ambitions. You can have a very nice tank with any dKH. If you are striving to grow lots of stems and sensitive species then the lower the dKH the better. So would I recommend it? I guess it depends on how far down the rabbit hole they want to jump.

    And keep in mind most pH problems are related to maintenance. If someone gets into the hobby and doesn't understand or want to perform maintenance then they are likely going to have lots of problems regardless. Tanks dKH makes little difference. If the tank is in such poor shape that the they have a pH crash a bit more dKH isn't likely to save them. The same forces are at work, will just take less time to get there at lower dKH.

    With even reasonable maintenance and water changes there is little to worry about. Most of the times you hear people talk about pH crashes it's something they have read, not experienced. You have to REALLY neglect a tank for it to happen. I mean no water changes, over feeding, lots of dead/decaying plant matter. Basically if that's they case the are in the wrong hobby.
     
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    I agree with Gregg’s comments. The only reason I run 1dKH is my Milwaukee controller stops at 5.5ph. At 1dKH, my RO water measure3s about 6.7-6.8 so the 5.5 makes a nice natural stopping point.
    The fun part was dialing in the flow meter to consistently get me to 5.5 without going any lower (air stones and surface agitation all come into play as well). System has been working perfectly for a few years now.
     
    The situation is different for me. I guess I would be a reluctant 0KH tank keeper. My KH is 0 out of the tap. The last couple times I have set up a new aquarium, I'd do my daily water changes at first and no problem for a few weeks. Then all the sudden I'd go in one morning and all the tissue from my plants would be gone and all that would be left was white dead material from the thickest parts of the plants. I would have a random pH crash. I didn't know what it was, but after the second time a friend helped me out. From then on the maintenance on the tank would suck because of the dead material dumping so many nutrients and organics into the water.
    I would prefer to keep my KH at ~2, but I have been using Aquasoil and any bicarb I put into the water gets absorbed quickly. Last setup I had Seriyu Stone and that helped a lot, but it didn't fix the problem 100%, and I crashed my tank. I think it crashed one time when it was fairly established also. It's been awhile. I can't remember anymore.
    At the AGA I sought out people who might have some thoughts on what to do. Luis had a good suggestion. I'll try it next time I set the tank up. It's been dry awhile now out of frustration of killing all the plants a couple times. I'm getting the itch again though..... :)
    (Disclaimer no fish were harmed in any tank crashes because I didn't want to fool with them and never bought any in a couple years of having the tank set up.)
     
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    Ben - sorry that sounds really strange to me. In the reefing hobby, there is a concept called rapid tissue necrosis (RTN) that happens to corals extremely quickly. However, I've rarely seen this on the freshwater planted side.

    I don't think a pH crash would be responsible for this either. Things simply don't happen that quickly in a planted tank, IMO.

    When I have seen something similar to what you're describing, it's been chlorine/chloramine issue. Do you use tap water for your system?
     
    The fun part was dialing in the flow meter to consistently get me to 5.5 without going any lower (air stones and surface agitation all come into play as well). System has been working perfectly for a few years now.
    OK so you need to explain this to me. I know @GreggZ has a flow meter also. I've never set one up for this purpose.

    My setup is using an aquarium controller with a pH probe to control CO2 addition. How do you work a flow meter into this?
     
    If the tank is in such poor shape that the they have a pH crash a bit more dKH isn't likely to save them. The same forces are at work, will just take less time to get there at lower dKH.
    So you raise a good point. I guess the way I think of things is that low dKH is dangerous for a newbie because they tend to run their aquariums "dirtier" than more experienced folks. By having moderate dKH, they have a bit more margin of error.
     
    The situation is different for me. I guess I would be a reluctant 0KH tank keeper. My KH is 0 out of the tap. The last couple times I have set up a new aquarium, I'd do my daily water changes at first and no problem for a few weeks. Then all the sudden I'd go in one morning and all the tissue from my plants would be gone and all that would be left was white dead material from the thickest parts of the plants. I would have a random pH crash. I didn't know what it was, but after the second time a friend helped me out. From then on the maintenance on the tank would suck because of the dead material dumping so many nutrients and organics into the water.
    I would prefer to keep my KH at ~2, but I have been using Aquasoil and any bicarb I put into the water gets absorbed quickly. Last setup I had Seriyu Stone and that helped a lot, but it didn't fix the problem 100%, and I crashed my tank. I think it crashed one time when it was fairly established also. It's been awhile. I can't remember anymore.
    At the AGA I sought out people who might have some thoughts on what to do. Luis had a good suggestion. I'll try it next time I set the tank up. It's been dry awhile now out of frustration of killing all the plants a couple times. I'm getting the itch again though..... :)
    (Disclaimer no fish were harmed in any tank crashes because I didn't want to fool with them and never bought any in a couple years of having the tank set up.)
    Ben I take it you are talking about setting up new tank with fresh aquasoil? If so most likely the plants crashing was from ammonia. Did you remove the dead/decaying plant matter? I ask because you mentioned all off the nutrients and organics in the system from the dying plants.

    And when you say a pH crash, what did the pH drop to? Did you actually measure it? Or did you assume it was a pH crash?

    Just saying this sounds very unusual and there are loads of people all over the world who set up new tanks with RO and aquasoil and don't experience anything like this. Assigning cause and effect is sometimes difficult to pinpoint, and in this case I am guessing it was something else.
     
    OK so you need to explain this to me. I know @GreggZ has a flow meter also. I've never set one up for this purpose.

    My setup is using an aquarium controller with a pH probe to control CO2 addition. How do you work a flow meter into this?
    Art the advantage of a flow meter is to keep a more consistent CO2 flow. Many needle valves suffer from drift over time. If I set my flow meter to 45 cc/min it stays there. It also allows for better fine tuning. Let's say I want to increase flow from 45 to 50 cc/min. Very easy with a flow meter. With a needle valve and counting bubbles it's very difficult to fine tune in small increments.

    So you raise a good point. I guess the way I think of things is that low dKH is dangerous for a newbie because they tend to run their aquariums "dirtier" than more experienced folks. By having moderate dKH, they have a bit more margin of error.
    Yes some depends on the dedication and ambitions of the newbies. But the pH swing difference between zero and 1 or 2 dKH is minimal. Just saying if the tank is dirty and neglected enough the little bit of carbonates won't save someone. Again to create a pH crash you need to have a REALLY dirty tank. It would be interesting for someone to set up an experiment to cause a pH crash. My feeling is that it would be a LOT harder than you think to induce one.
     
    Art the advantage of a flow meter is to keep a more consistent CO2 flow. Many needle valves suffer from drift over time. If I set my flow meter to 45 cc/min it stays there. It also allows for better fine tuning. Let's say I want to increase flow from 45 to 50 cc/min. Very easy with a flow meter. With a needle valve and counting bubbles it's very difficult to fine tune in small increments.
    Thanks, Gregg. I can certainly understand and agree with this.

    For a very long time, I would target pH using the probe and not rely on a bubble count or flow rate (in your situation). I would open the needle valve enough to get a reasonably fast pH decrease to what I want during the day and let it go at that. I don't think a flow meter would be useful in my situation.
     
    OK so you need to explain this to me. I know @GreggZ has a flow meter also. I've never set one up for this purpose.

    My setup is using an aquarium controller with a pH probe to control CO2 addition. How do you work a flow meter into this?
    I'll give this a shot :)
    Back on TPT a really smart guy figured out there are lab grade flow meters that will work nicely for our CO2 purposes.
    When you have a larger tank, a bubble counter is useless.
    The flow meter has a scale on it and if the rest of your CO2 equipment is of good enough quality (another variable I can add), you can consistently add an exact amount of CO2 to your aquarium until your CO2 tank runs out.

    I basically used the pH controller readout to get me close to the drop I wanted. (think, I know I need more than 7 on the flow meter, but 9 makes my fish gasp). Eventually I find that 8.25 on the flow meter gives me a 1.2-1.3pH drop in the tank. "IF" the CO2 tank has enough, "IF" the regulator holds exactly 20psi, "IF" I don't bump one of the metering valves (yes I have more than 1).

    As long as all the "IF's" are where they need to be - there really is no need for a pH controller.

    But, what if you bumped something... setting the pH controller with an absolute bottom number prevents the fish from getting a lethal dose of CO2.

    Also, like Gregg, I have air stone(s) on digital timers. Add 10 minutes of air stone each hour and I add a little more O2 "and" keep the pH at exactly the same amount the entire day.

    And for what's it worth - pics :)
    Porter Flow Meter, Whitey high precision valve, CO2 reactor w/by pass, Victor regulator
     

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    Sorry for the late reply. I worked a few rare third shifts last week, and we had daylight savings. My brain is still slowly coming back online. I am not Dr Who, and I don't time travel well.

    When I have seen something similar to what you're describing, it's been chlorine/chloramine issue. Do you use tap water for your system?
    Yeah, I use tap water. The KH of my tap is 0. I put chlorine/chloramine remover in my aquarium before I add the fresh water. I don't think we have chloramine in our water here.

    Ben I take it you are talking about setting up new tank with fresh aquasoil? If so most likely the plants crashing was from ammonia. Did you remove the dead/decaying plant matter? I ask because you mentioned all off the nutrients and organics in the system from the dying plants.
    Yes, it was a new Aquasoil tank the first time, but I was changing water (50%) daily in the first 10 days or so to limit the ammonia build-up. Also, I said the build-up of organics and nutrients was after the crash. The build-up happened because everything died and made maintenance difficult from that point on. The second time it was also an Aquasoil tank, but it happened much later in the process and not at the beginning.

    And when you say a pH crash, what did the pH drop to? Did you actually measure it? Or did you assume it was a pH crash?
    No, I never tested it. I didn't know what was happening, so it wouldn't occur to me to test it. I described what happened to Ghazanfar and Luis and they felt that was what was going on. I had no idea.

    Just saying this sounds very unusual and there are loads of people all over the world who set up new tanks with RO and aquasoil and don't experience anything like this. Assigning cause and effect is sometimes difficult to pinpoint, and in this case I am guessing it was something else.
    Yeah, that's my experience also. I had never had it happen before until these 2-3 times. I am going on the diagnosis of 2 masters of the hobby and I might have run it by other people, but it's been a while and my brain is getting fuzzy.
     
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    So why does supposed 0 KH work and there's no pH crash that's been promoted for the last 40 years? At least since the 1980's with the Dupla Book and poor KH understanding by aquarist.

    Thought experiment time: I have a plant tank with a KH of say 1 degree, 17.68 ppm. I add enough CO2 to get say a pH of 5.6. 75ppm according to the pH/KH/CO2 assuming the 17.68 is all bicarb alkalinity. So I do a 50% water change with pure RO with a conductivity of 8 uS. So now I'd down to a KH of 0.5 KH degrees pH of 5.3 and a CO2 of guess what? 75 ppm. I cut this tank water with another 50% with the pure RO, now I'm down to 0.25 KH. So I;ll cut this again by 1/2 with that pure RO, 4.7 and .125KH. and you guessed it, 75 ppm CO2. The FLOW, the amount of CO2 gas being added is the same in all 4 states. Does ANYONE disagree on that point? You should not.

    So the rate of CO2 gas being added is the same (measured say mls of gas/minute etc, easy to measure underwater, no?) and can be set pretty accurately and stable, then you just remove the remaining KH.
    The CO2 being delivered to plants will be the same in all 4 cases, even if you remove ALL the KH within reason.
    As the KH is the only variable you are changing, you assume the CO2 is the same.

    Some suggest there's no base for the CO2 acid when it turned to H2CO3, carbonic acid. Well, it's a rather weak acid in fact, it's not completely changed, only 1 out of 400 molecules change, the rest of the gas is dissolved CO2 [aq], THAT is what the plant takes up as a carbon source and uses inside the spongy mesophyll leave cells. So this means only 0.25% of the KH is needed for base. So this is about 0.045 ppm of KH, not much. Even less than this, you still get a partial buffering.

    So measuring the KH and the CO2 might be hard, but you can adjust things at say 0.5 dKH, then once set, remove it with RO. The ppm to the plants should be the same in both cases. Folks get mucked up with the chem, acid base stuff etc. Do not feel bad, I've had PhD chemist mess this up. The typical nutrocentric hobbyist is more than likely to get it mixed it too.

    But this discussion helps folks focus better on CO2 and with less fear.
     
    So why does supposed 0 KH work and there's no pH crash that's been promoted for the last 40 years? At least since the 1980's with the Dupla Book and poor KH understanding by aquarist.

    Thought experiment time: I have a plant tank with a KH of say 1 degree, 17.68 ppm. I add enough CO2 to get say a pH of 5.6. 75ppm according to the pH/KH/CO2 assuming the 17.68 is all bicarb alkalinity. So I do a 50% water change with pure RO with a conductivity of 8 uS. So now I'd down to a KH of 0.5 KH degrees pH of 5.3 and a CO2 of guess what? 75 ppm. I cut this tank water with another 50% with the pure RO, now I'm down to 0.25 KH. So I;ll cut this again by 1/2 with that pure RO, 4.7 and .125KH. and you guessed it, 75 ppm CO2. The FLOW, the amount of CO2 gas being added is the same in all 4 states. Does ANYONE disagree on that point? You should not.

    So the rate of CO2 gas being added is the same (measured say mls of gas/minute etc, easy to measure underwater, no?) and can be set pretty accurately and stable, then you just remove the remaining KH.
    The CO2 being delivered to plants will be the same in all 4 cases, even if you remove ALL the KH within reason.
    As the KH is the only variable you are changing, you assume the CO2 is the same.

    Some suggest there's no base for the CO2 acid when it turned to H2CO3, carbonic acid. Well, it's a rather weak acid in fact, it's not completely changed, only 1 out of 400 molecules change, the rest of the gas is dissolved CO2 [aq], THAT is what the plant takes up as a carbon source and uses inside the spongy mesophyll leave cells. So this means only 0.25% of the KH is needed for base. So this is about 0.045 ppm of KH, not much. Even less than this, you still get a partial buffering.

    So measuring the KH and the CO2 might be hard, but you can adjust things at say 0.5 dKH, then once set, remove it with RO. The ppm to the plants should be the same in both cases. Folks get mucked up with the chem, acid base stuff etc. Do not feel bad, I've had PhD chemist mess this up. The typical nutrocentric hobbyist is more than likely to get it mixed it too.

    But this discussion helps folks focus better on CO2 and with less fear.
    Well said as usual my friend. Like many of our discussions, my conclusions are largely anecdotal, while you actually have science to back things up!
     
    The typical nutrocentric hobbyist
    I love this. I'm going to borrow this say, Tom. I will give you credit. LOL

    So, well said. I love how you brought in the fear some newer hobbyists feel with CO2 additions and water parameters.

    My question for you: Is there any time that you would think some moderate amount of KH is better in a planted aquarium?

    And, thanks for commenting, Tom.
     
    Would you guys recommend to a newbie to go zero KH?

    It depends on their ambitions.

    I would absolutely recommend it with the only concession being to Gregg's point. Do they want to get their hands wet and go down the rabbit hole? Then absolutely. My first tank was low-to-no kh, and I knew nothing about plants or tanks--never so much as kept a bowl with rainbow gravel in it even. I never ran into any problems with 0dkh, probably because of a couple other points brought up here (regular basic maintenance and a bit of reading and research)

    @plantbrain also appreciate you commenting here Tom, I honestly didn't know the ppm of injected co2 would be the same regardless of KH. That was super interesting to read, I have to sharpen up my rudimentary water chemistry knowledge somewhere along the line.

    @GreggZ we have similar thoughts about CO2 setups I think, I've never ran a monitor because my ph dips too low on injection to be of any practical use. I finally upgraded my setup with a nicely built reg and the biggest thing I sprang on were two very good needle valves and some metered handles for them, think everyone knows what I'm talking about without adding a pic...now I have a point of reference on the valve handle itself so I have an arbitrary number that says *this* is where you were getting your 1.4 drop with equipment arranged the way it was, etc...instead of having to guess or rely on a bubble counter.

    The flow meter sounds like it solves the exact same issue that the handles did for me, but maybe in an even more efficient way. How easy or difficult are they to incorporate into a reg you already have, are they just screwed in with their own built-in needle valve, etc? It's something I'd like to look into adding to my setup
     
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