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Ph profile, co2 and 0kh

_Maq_

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We're not doing a PhD thesis here.
It's quite simple, though. One degree drop in pH means tenfold increase of CO2 content, but you can't take for granted that outgassed water contains 3 ppm CO2. It depends, among others, on alkalinity.
If you would have quoted my full sentence, the argument would be entirely different.
My apology, I've obviously misunderstood your point. Yes, I agree, a water with very low alkalinity is prone to unexpected changes in pH. Plenty of personal experience. :)
 

LMuhlen

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It's quite simple, though. One degree drop in pH means tenfold increase of CO2 content, but you can't take for granted that outgassed water contains 3 ppm CO2. It depends, among others, on alkalinity.:)
The general idea of measuring degassed water pH is that we assume that the CO2 concentration is in equilibrium with the atmospheric CO2 concentration, and that doesn't depend on what is in your water. There is some discussion regarding this notion that this equilibrium is close to 3ppm, but that usually is because the atmospheric concentration could change in different indoor environments.

Now from what I understand of this discussion, the core of the discrepancy is the same that popped in my CO2 topic, if the DIC equilibrium applies only to one tiny fraction of dissolved carbon, the part that forms carbonic acid, or if it applies to the entire carbon population, making it so that high pH water in equilibrium has no CO2 and only carbonates and bicarbonates.
 

GreggZ

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While my stock seem completely happy, I am a bit on edge.
IMO no need to be on edge. Myself and many others have been running pure RO very little to no dKH tanks for years. There are loads of myths out there that still get repeated over an over. Most times it's from people who have never run a low dKH planted tank.

My fully degassed pH is 6.25 and I drop pH via CO2 injection to 4.85 on a daily basis. The readings are always very stable. My Rainbowfish show no signs of distress. However if I drop any much further they do begin to get lethargic.

That is the same at any dKH. There is always a limit where fish will show distress. It varies a bit from tank to tank but I believe that has more to do with oxygen levels. CO2 and O2 are not mutually exclusive. The higher the O2 concentration the higher the CO2 concentration can be without affecting livestock.

The people I know who run tanks in this fashion do not experience a pH crashes. They have no problem with nitrifying bacteria dying. Fish do not die from osmotic shock.

And it's not to say that pH crashes are not real. They are almost always tied to very poor maintenance. A well run clean tank at zero dKH has nothing to worry about.

Here's an article from the 2 hr Aquarist site regarding low pH tanks. My tank is pictured from several years back when I was running 1 dKH. Shortly after that article I stopped dosing any carbonates at all and not a thing changed other than the degassed pH level.

 
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plantnoobdude

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IMO no need to be on edge. Myself and many others have been running pure RO very little to no dKH tanks for years. There are loads of myths out there that still get repeated over an over. Most times it's from people who have never run a low dKH tank planted tank.

My fully degassed pH is 6.25 and I drop pH via CO2 injection to 4.85 on a daily basis. The readings are always very stable. My Rainbowfish show no signs of distress. However if I drop any much further they do begin to get lethargic.

That is the same at any dKH. There is always a limit where fish will show distress. It varies a bit from tank to tank but I believe that has more to do with oxygen levels. CO2 and O2 are not mutually exclusive. The higher the O2 concentration the higher the CO2 concentration can be without affecting livestock.

The people I know who run tanks in this fashion do not experience a pH crashes. They have no problem with nitrifying bacteria dying. Fish do not die from osmotic shock.

And it's not to say that pH crashes are not real. They are almost always tied to very poor maintenance. A well run clean tank at zero dKH has nothing to worry about.

Here's an article from the 2 hr Aquarist site regarding low pH tanks. My tank is pictured from several years back when I was running 1 dKH. Shortly after that article I stopped dosing any carbonates at all and not a thing changed other than the degassed pH level.

My concern was in relation to co2 causing live stock stress, and not with ph crashes.
None the less, thank you for your advice.
 

Hanuman

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Hi, in my high tech 60p I maintain soft water with 0kh and also inject co2.

Though 1.0ph drop is generally regarded as optimal and safe for live stock, does this still apply for tanks with no kh? I recently checked my tank pH and degas pH.

24h Degas sample is 6.65-6.7
Tank values stay from
5.2-5.3 throughout the day so far.
This means I have a ph drop of 1.4!!!

I was wondering, since I don’t have any buffer, is it possible I have less co2 in terms of ppm in the water, compared to say a tank with a kh of 4 with the same pH drop?

While my stock seem completely happy, I am a bit on edge.

Thanks!
No problems on this side of the earth.

1.4 PH drop from 6.38 down to 5 or slightly lower. 0 dKH reading. Everyone happy. Never been on edge. Drop checker yellow like urine. This said, if I had to wack a lot of plants from the tank I would slightly reduce Co2 injection to be safe.

Take a beer and relax.
 

Yugang

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You don't need to raise the dKH.

There are a number of difficulties with pH measurement and interpretation, pH is both a ratio and a <"log10 scale">.

Stable pH only exists in very heavily buffered water. As you approach pure H2O pH becomes less and less meaningful. In soft waters pH will always be a movable feast, and you can't extrapolate from sea water or Lake Tanganyika to soft water.
I look on changes in pH in another way, I just say "does this change in pH reflect a large change in the chemistry (number of ions) in the water?"

As long as the answer is "no" (like in your added CO2 scenario) then it isn't going to bother the fish. Have a look at the <"A question, dissolved...> thread for an example of pH fluctuations due to dissolved gases.
This is from a usefull thread.

(As a non-chemist, and happily at KH 2) I take it that in realistic situations in a tank (KH probably not exactly zero, substrate and all the other stuff), with fish as the ultimate judge, we should't worry about CO2 injection at KH close to 0 as long we maintain the tank well. And of course all the usual precaution associated with CO2 as in any other tank.

For laboratory situations, less practical relevant, we have a case that pH does strange things at kH 0, and our usual logic using pH as a proxy for CO2 may not apply ('applies even less').
 
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Hanuman

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Yes, when people using RO say 0 dKH they mean they don’t add any carbonates either intentionaly through chemicals or through the addition of heavily loaded carbonate stones like seryu stones. Now this usually doesn’t mean there isn’t any carbonate in the water. The soil will actually contain some carbonates. If the tank had actually 0dKH I think you would not be able to see any snails and your PH would actually swing, but most dKH test are not sensitive enough to detect lower amounts of carbonates hence why we say 0dKH.
 

plantnoobdude

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“Note 2: The pH-KH relationship is not linear. If your tank water measures 0-1dkH, you need to target around a 1.5pH relative drop to be within reach of the 25ppm CO2 target.”

From Dennis. This little tidbit of information is quite interesting, since it links my 1.4 pH drop to my green drop checker. Quite interesting, I wonder how he arrived at this conclusion.

The article for anyone interested
 

Freshflora

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“Note 2: The pH-KH relationship is not linear. If your tank water measures 0-1dkH, you need to target around a 1.5pH relative drop to be within reach of the 25ppm CO2 target.”

From Dennis. This little tidbit of information is quite interesting, since it links my 1.4 pH drop to my green drop checker. Quite interesting, I wonder how he arrived at this conclusion.

The article for anyone interested
You can email the 2hr aquarist team or fb message him. I’ve done both multiple times and he’s always responded.
 

Yugang

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pH-KH relationship is not linear.
The formula that I use is CO2 = 12.839 * dKH * 10^(6.37 - pH). Indeed the relationship pH to CO2/dKH is logarithmic, not linear. It is important to understand that also outgassed pH is not a constant, but dependant on KH and ambient air CO2 concentration.
Most importantly, a given pH drop (from degassed) will indicate an X% CO2 increase, irrespective of KH. (pH drops 1.0, means 10 fold CO2 compared to starting CO2, from the above formula). This is also true for KH below 1, from all references that I've seen.

if your tank water measures 0-1dkH, you need to target around a 1.5pH relative drop to be within reach of the 25ppm CO2 target.
This is really the first time that I read this, good catch @plantnoobdude , this is most likely not correct. Indeed good to reach out and ask for clarification.

Many hobbyists are around 1.4 drop ( I do 1.5 without any problem), and if fish are happy there is not much reason to worry. Fish could also be unhappy at a pH 1.0 drop, so what's in a number ... Let the fish talk (and check drop checker as well) is what I learned

And for the plants .... CO2 stability is what counts, more than the absolute value. Unless we flood the tank with light, there is no confirmed benefit pushing the CO2 too high. This is important to remember, before we go into the rabbit hole of measurements and formulas.
 
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Yugang

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the rabbit hole of measurements and formulas
See attached.

The formula I quoted above is what I found a couple of years ago, but when I search again not sure if there is consensus on that one. I used it for a model to estimate CO2 in my tank, and it was at the time good enough for what I wanted to do. The point is that absolute CO2 value matter less than stability, so why would we want to know precisely?

Simplicity first. Keep fish safe and CO2 stable :)
 

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  • Chemistry CO2 in water.pdf
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Yugang

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That post just plots out the well know logarithmic relationship. Basically what the CO2/pH table does, but then in a graph.

We're not doing a PhD thesis here.
My view is that the topic is made unnecessarily complicated. Let me explain.

pH drop is a proxy for CO2. This means that a pH curve can be used to estimate what CO2 is doing, an indication of the absolute value and most importantly if it is stable. It is not a guarantee that the measurement is super accurate, indeed other chemicals can cause some perturbations and it is always possible to find situations where one should be cautious with conclusions.

Is it a problem using a proxy? Well, infact every measurement in science or technology is a proxy. There is no direct way to tell how tall you are, how old are fossils, or how far Alpha Centauri is from us. Basically these are all estimations based on observations, with many things that could potentially go wrong.

So back to the CO2/pH table. Yes it is a proxy, and chemists are happy to point out that things can go wrong and the measurement is not super accurate. The point is that the alternatives are worse. A professional CO2 probe is too expensive, so it is not of any practical value for most of us. And have you ever tried to accurately read out a drop checker to estimate what the weighted average of pH was over the last 3 hours?

So now back to basics. The CO2/pH table is the best proxy we have for practical purposes, and the general advice is to target 1.0 pH drop. It is not relevant for our practical aims that our proxy may be a bit off, as we don't care too much about absolute numbers but we care a lot about stability over time.

Most likely a (large) majority of high tech tank keepers are not using pH probes, and have therefore no idea how much instability they have in their tank. They tweak ferts and light, but the CO2 stability is the elephant in the room. The theoretical debate about the pH/CO2 relationship has much less practical value than a good focus on that big elephant in the room.

In fact the theoretical discussion takes our eyes off the ball and confuses. Until we have an affordable and better alternative to pH probes and drop checkers.

(nothing personal @_Maq_ , I know you like a good debate :))
 

PARAGUAY

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Fish happy. Plants happy. This means bacteria happy. Water crystal clear? No need to worry. :).

I am amidst rescaping my tank and debating removing all testing including DC and running co2 just by the system.
Why no drop checker Josh?
 

JoshP12

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Why no drop checker Josh?
Always found it makes me second guess. Also found it distracts from the tank.

Ex:
Fish looks lethargic but it’s green — no brainer turn it down … but it’s green so it’s fine?

Ex:
Everything looks great! But it’s blue - gotta turn up co2.

Caught myself down these rabbit holes too many times - including pH.

Who knows I might re introduce it.

But before I went hands off with my tank I found it to be much simpler: turn co2 on and look at tank, turn it up, look at tank. Fish unhappy, turn it down.

Co2 with lights or 1 hour before lights. Lights just on or 30 min ramp. up and down.

Tank still looks bad? Turn down ferts (use some starting point) and/or increase water change/maintenance frequency until you find balance. Lol

Going to try it and that means no drop checker, probes etc. :).
 
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