How to manage CO2 overnight - Page 3 - The Planted Tank Forum
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post #31 of 40 (permalink) Old 09-05-2019, 02:10 AM
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Originally Posted by Deanna View Post
Although I no longer use them, I think dcís are going to be delayed even if CO2 and pH is consistent. A change in either will still be very slow to show up.
Drop checker delay issue is irrelevant when CO2 is injected 24/7 and when aeration keeps dissolved CO2 stable. The use of a pH tester is to show possible fluctuations, and the drop checker to display the real CO2 concentration via water to gas interface. What I do is simply hookup passive reactors for small aquariums or CO2 reactors with gas flow meters and drop checkers for large. Besides, the pH drop idea is misleading, some people have difficulties with fish at 1.0 pH drop while others can have 1.7 pH drop without problems. More fun here.

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You mentioned that you counter the nighttime tendency for CO2 to rise, by increasing aeration. Is this done with an aerator on a timer? If so, how would decide when to turn it on and off?
No, that would be risky, complicated and unnecessary. I run aeration continuously and have CO2 concentration stable at appropriate level with very low CO2 gas flow. Very consistent and safe.

Last edited by Edward; 09-05-2019 at 02:14 PM. Reason: ...
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post #32 of 40 (permalink) Old 09-05-2019, 03:09 AM
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Remember that we are talking about a fixed KH of 6 (Dennisí example) and zero CO2.
No. ph=~7.8 is for 3ppm CO2 thereabouts with rounding and what degassed samples should have in them when in equilibrium at 25C and whatever the atmospheric pressure they assumed in the theory.


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You can try it by taking RO water and hitting the KH 6 point. As you know, the pH will be 7.8. Now, add some lemon juice to it, pH drops and so does KH.
Adding a strong acid does drive off CO2 and lower kH irreversibly, but that is not how you arrive at kh=6 ph=7 equilibrium.

We do not know what buffers are in his water including weak acids in addition to carbonates, but his water equilibrium exists and measuring CO2 with the charts is not accurate as a result.

It is no different from my water, by Carbonate theory my degassed tap water is kh=4-5 and should be ph=7.6 - 7.7 but in reality it fluctuates between 8 - 8.2. I can achieve my tap water kh and ph by adding a weak base in addition to carbonates to my RO water.

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Forgetting the potential natural drift caused by other weak acids, if we maintain KH of 6, we canít maintain a pH of 7. This is why I donít quite get what Dennis is saying in that example.
You can't forget other weak acids or buffers that is the whole point, it isn't RO water with carbonates in it, it is an equilibrium that is more complicated so the Barr Chart cannot be used accurately.

In his situation the best assumption is drop his ph to 6.0 to get 30ppm of CO2. It isn't a perfect assumption but its the best that we can do as hobbyists with limited equipment that was Dennis's suggested method and point.

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If my pH changes by 1 point with only CO2 as the flywheel, we do know that this is closer to 30ppm of CO2 than 50ppm of CO2. If my KH levels move my pH levels according to prediction, then I know that more than a one-point pH change due to CO2, when it should be one point, is an indication of a faulty pH meter or KH test results. Then, I calibrate my pH meter. This is the corroboration.
That assumes your CO2 injection rate is stable, as is your kH, and that you aren't adding any organic acids (like Tannins etc) or bases.

However if you are making the argument that 1ph is closer to 30ppm than 50ppm than you have to also admit that 0.1ph cannot be assumed to be 10ppm.


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post #33 of 40 (permalink) Old 09-05-2019, 03:38 AM
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No. ph=~7.8 is for 3ppm CO2 thereabouts with rounding and what degassed samples should have in them when in equilibrium at 25C and whatever the atmospheric pressure they assumed in the theory.




Adding a strong acid does drive off CO2 and lower kH irreversibly, but that is not how you arrive at kh=6 ph=7 equilibrium.

We do not know what buffers are in his water including weak acids in addition to carbonates, but his water equilibrium exists and measuring CO2 with the charts is not accurate as a result.

It is no different from my water, by Carbonate theory my degassed tap water is kh=4-5 and should be ph=7.6 - 7.7 but in reality it fluctuates between 8 - 8.2. I can achieve my tap water kh and ph by adding a weak base in addition to carbonates to my RO water.



You can't forget other weak acids or buffers that is the whole point, it isn't RO water with carbonates in it, it is an equilibrium that is more complicated so the Barr Chart cannot be used accurately.

In his situation the best assumption is drop his ph to 6.0 to get 30ppm of CO2. It isn't a perfect assumption but its the best that we can do as hobbyists with limited equipment that was Dennis's suggested method and point.



That assumes your CO2 injection rate is stable, as is your kH, and that you aren't adding any organic acids (like Tannins etc) or bases.

However if you are making the argument that 1ph is closer to 30ppm than 50ppm than you have to also admit that 0.1ph cannot be assumed to be 10ppm.
I think we're saying the same thing. There is no precision in any of this, not least of the reasons being that not only do we not know what is in our own tanks, but we will never be able to guess what is in anothers' tank. I don't think he can say that you can have KH 6 and pH 7 without building an entire framework of possible interference in the real world. This doesn't rule out a KH/pH analysis in favor of any other means of estimating CO2, other than directly measuring CO2.
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post #34 of 40 (permalink) Old 09-05-2019, 03:50 AM
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Drop checker delay issue is irrelevant when CO2 is injected 24/7 and when aeration keeps dissolved CO2 stable. The use of a pH tester is to show possible fluctuations, and the drop checker to display the real CO2 concentration via water to gas interface. What I do is simply hookup a passive reactor for small aquariums or gas flow meters with drop checkers for larger. Besides, the pH drop idea is misleading, some people have difficulties with fish at 1.0 pH drop while others can have 1.7 pH drop without problems. More fun here.

No, that would be risky, complicated and unnecessary. I run aeration continuously and have CO2 concentration stable at appropriate level with very low CO2 gas flow. Very consistent and safe.
That's right: I forgot about your passive reactor. IME, fish are going to struggle at any significant level of CO2, initially, until adapted. I've run at about 1.5 drops without fish strain and also have found that they have as much trouble re-adapting back up to these higher levels after easing off to less than 1 drop. I do suspect that they are uncomfortable in the 30ppm area, otherwise no adaption would be needed.

I'm having difficulty seeing how constant aeration at a constant level, along with a constant rate of CO2 is going to allow for consistent CO2 levels. If plants take more during the day and less at night, how can the level of CO2 not be higher at night? Perhaps the real answer is in that absence of fluctuation point you mentioned.Maybe it is more important than a high CO2 level, i.e.; keeping it more or less consistent 24/7 provides a sweet spot that is much lower than 30ppm.

Yes: dc level won't change if CO2 doesn't change, so delays in response aren't measurable (nothing to measure).
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post #35 of 40 (permalink) Old 09-05-2019, 04:27 AM
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This doesn't rule out a KH/pH analysis in favor of any other means of estimating CO2, other than directly measuring CO2.
We'll have to agree to disagree on this.

There are many threads on this topic, you may want to read them, I am just paraphrasing what has already been said.
https://www.plantedtank.net/forums/1...l#post10075082

Just because you can't understand how he can have kh=6 and ph=7 water, which he does, isn't really important it doesn't validate that chart.

That Tom Barr Chart is flawed, it uses one single formula for every value in the chart which makes it rubbish.
CO2= 3*kh*10^(7-ph) do the calculation for any values in the chart to confirm.

Simple put, my reccomendation matches Dennis's, ignore the chart and kH(provided it is 1 - 10), and take your degassed value and look for a drop of 1ph that would be ~30ppm. That is pretty much all anyone can do here.

It isn't accurate over the whole ph range, you should adjust if you have high or low atmospheric pressure, CO2 isn't linear with ph, and a bunch of other caveats but that is a solid starting point, blindly reading off the Tom Barr chart is not.

What is important is that someone doesn't blindly read off the charts and assume their tap water has 20ppm even before they start to inject CO2.


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Last edited by cl3537; 09-05-2019 at 05:15 AM. Reason: ...
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post #36 of 40 (permalink) Old 09-05-2019, 12:15 PM
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Bet y'all can guess who got suspended for 10 days.

If you want to insult other members? You'll get suspended or banned.

This is a PLANT FORUM. A damn plant forum. Quit acting like it's life or death.


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post #37 of 40 (permalink) Old 09-05-2019, 05:22 PM
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What I meant to say was; I use passive reactors for small aquariums or CO2 reactors with gas flow meters and drop checkers for large.

Passive reactors are self-regulating by design, nothing to worry about. But CO2 reactors can overdose CO2 so they need gas flow control and drop checkers when used 24/7. I prefer drop checkers because they display CO2 concentrations better than pH probes in 0 – 1 dKH water.

It is reasonable to believe that fish may not be very happy about pH, dissolved CO2 gas and oxygen concentration changes. Some say these are happening in nature too so what. Well, so are lightning strikes.

About aeration. Aeration is needed regardless of CO2 injection or not. Water with no gas exchange with atmosphere is dead water. When aeration is off and CO2 injection on, dissolved CO2 will go up for few days and could reach unhealthy levels, and will fluctuate with lights on and off. Can’t have that. But with little aeration on, CO2 concentration will stabilize in two days and will not go any higher. This is because the aeration moves some CO2 from water to atmosphere. So there is equilibrium between CO2 delivery and CO2 outgassing. The outgassing rate is higher than plant’s CO2 uptake. Is it unnecessarily wasting gas? Well, we have to have little aeration for healthy gas exchange. And because the aeration removes more CO2 than plants use, the CO2 concentration becomes consistent and plant’s CO2 uptake irrelevant.

Is it difficult? No because the CO2 flow rate is very low compared to CO2 with lights on only. This is not fast so there is plenty of time. The only thing is to set very low aeration that doesn’t remove too much dissolved CO2. This can be determined by reading pH or drop checker.

What is also helping to self-regulate this is that it takes disproportionally more gas to achieve higher concentration. Similarly, outgassing rate is higher at higher concentration.



The small pH fluctuation is caused by pH reading inaccuracies and temperature variations.


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Last edited by Edward; 09-05-2019 at 05:23 PM. Reason: ...
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post #38 of 40 (permalink) Old 09-05-2019, 08:02 PM
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About aeration. Aeration is needed regardless of CO2 injection or not. Water with no gas exchange with atmosphere is dead water. When aeration is off and CO2 injection on, dissolved CO2 will go up for few days and could reach unhealthy levels, and will fluctuate with lights on and off. Canít have that. But with little aeration on, CO2 concentration will stabilize in two days and will not go any higher. This is because the aeration moves some CO2 from water to atmosphere. So there is equilibrium between CO2 delivery and CO2 outgassing. The outgassing rate is higher than plantís CO2 uptake. Is it unnecessarily wasting gas? Well, we have to have little aeration for healthy gas exchange. And because the aeration removes more CO2 than plants use, the CO2 concentration becomes consistent and plantís CO2 uptake irrelevant.

Is it difficult? No because the CO2 flow rate is very low compared to CO2 with lights on only. This is not fast so there is plenty of time. The only thing is to set very low aeration that doesnít remove too much dissolved CO2. This can be determined by reading pH or drop checker.

What is also helping to self-regulate this is that it takes disproportionally more gas to achieve higher concentration. Similarly, outgassing rate is higher at higher concentration.

The small pH fluctuation is caused by pH reading inaccuracies and temperature variations.
OK. That chart is the type of drift that Iíve seen, at lower variations, and was wondering about, although I was attributing it to plant CO2 consumption rather than temperature since I had not seen any temp fluctuations greater than about 2 dF. However, itís been quite a while since I monitored temp, so thatís the next thing to do to see if my pH changes (albeit oh-so minor) show a correlation to temp changes.

Gas exchange in my tank is good, maybe high, because of the strong surface rippling that I target 24/7, so that is covered.

Iíll have to look into dcís again, since I do stay in the 1.1-1.3 dKH area and pH ~6-6.1 (stated as though I can measure at that level of precision). Are you saying that dcís are more responsive to slight pH changes at lower levels than at higher levels (as might be expected)? Makes sense given that low pH and low KH will show more dramatic changes with very little movement in either variable.

Do you use a 4 dKH reference solution?
What is your CO2ppm target?
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post #39 of 40 (permalink) Old 09-07-2019, 11:40 PM
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The pH fluctuation in the chart above shouldnít be because of plants uptake because the pH goes down when lights are on. Lower pH higher CO2. I know my CO2 pressure is not perfectly stable when room temperature changes, something the CO2 tank pressure regulator does. But still, having +/- 0.05 pH stability 24 hours a day without electronic pH controller is pretty good. Donít you think? Plant CO2 uptake doesnít affect it, evaporation does.

The probes we use have very high resolution and terrible accuracy, and our KH test kits have poor resolution and poor accuracy. When we combine these two and understand that many properties are affecting their results like unknown acids and carbonates, then we either use questionable formula or hoping for debatable pH drop theory to give us some kind of ppm of CO2? Too many variables can skew the result.

Drop checkers are very slow, have poor resolution but have very good accuracy. They are displaying exclusively what we are interested in, CO2. Sure they cannot be wired to pH controllers but with continuous CO2 injection they work well.

I donít use 4 dKH reference solution for simple reason my tap is always at 5 dKH. So it is simplicity for me, wash fill set. What is my CO2 target? Well, nobody knows how to measure dissolved CO2 gas or carbonic acid H2CO3 concentrations so what CO2 target Ö it comes down to plants not growing or fish in a bad mood. No not that. It takes little CO2 to have plants growing well, and it takes a huge amount of CO2 to have plants growing little faster.


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post #40 of 40 (permalink) Old 09-10-2019, 09:55 PM
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The pH fluctuation in the chart above shouldn’t be because of plants uptake because the pH goes down when lights are on. Lower pH higher CO2. I know my CO2 pressure is not perfectly stable when room temperature changes, something the CO2 tank pressure regulator does. But still, having +/- 0.05 pH stability 24 hours a day without electronic pH controller is pretty good. Don’t you think? Plant CO2 uptake doesn’t affect it, evaporation does.
Yes, that does seem to be pretty stable. I was under the impression that the drop in pH was temp related, but you explained that and, if room temp of the canister is varying, certainly the pressure is as well. In my case, my canister is in the basement and the ambient temp does not vary. So, is it your opinion that your CO2 level, whatever it is, does not change throughout a 24-hour period?

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The probes we use have very high resolution and terrible accuracy, and our KH test kits have poor resolution and poor accuracy. When we combine these two and understand that many properties are affecting their results like unknown acids and carbonates, then we either use questionable formula or hoping for debatable pH drop theory to give us some kind of ppm of CO2? Too many variables can skew the result.
I’m using a Hanna alkalinity colorimeter which, supposedly, has a tolerance of +/- 5%. When I calibrate to a 4 dKH solution (dilluted 40 dKH reference solution, since I’m getting back into dc’s), the colorimeter hit exactly 4 dKH and also calibrates exactly to the Hanna calibration solution they provide. So, I have very high confidence in the dKH level. They say that the only significant possibility for interference is chlorine (not chlorides) and I have no chloramines in my water.

PH could be another matter, as you said. However, I start with RO/DI and only add what we all know to add. How many weak acids the plants and other activity may be producing is an unknown, but with regular w/c’s may not be significant enough to skew pH readings. My meter calibrates quite well, but …who knows. As you and @cl3537 have mentioned, we may simply not be able to know how much of an influence all of the unknown variables may have on some of our test equipment, but can we get within a reasonable tolerance of a CO2 reading? Almost a rhetorical question.

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Drop checkers are very slow, have poor resolution but have very good accuracy. They are displaying exclusively what we are interested in, CO2. Sure they cannot be wired to pH controllers but with continuous CO2 injection they work well.

I don’t use 4 dKH reference solution for simple reason my tap is always at 5 dKH. So it is simplicity for me, wash fill set. What is my CO2 target? Well, nobody knows how to measure dissolved CO2 gas or carbonic acid H2CO3 concentrations so what CO2 target … it comes down to plants not growing or fish in a bad mood. No not that. It takes little CO2 to have plants growing well, and it takes a huge amount of CO2 to have plants growing little faster.
What color is your 5 dKH dc showing?
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