CO2 level without KH measurement

[bclee]

Actually you can estimate the CO2 level without measuring KH. It can be done by measuring the pH drop with and without CO2 injection.

A difference pH drop of about 1.6 to 1.7 will corresponds to injection of about 20-30ppm of CO2.

It can be done by measuring the pH of a CO2 enriched water sample from your tank. Drive out the CO2 by aeration or by standing the sample for prolong period say overnight or 24hrs. Measure the pH again. From this you can get the pH drop.

Any comments?

BC

[bclee]

To add... this will work will any KH values as long as it is not zero.

BC

[juggler]

Probably not for us who have slowly rising kH from using coral chips as a buffer.

[bclee]

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On 9/8/2003 5:34:08 PM

Probably not for us who have slowly rising kH from using coral chips as a buffer.
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No problem with that... only the pH difference is used. KH does not matter as long as it is not zero.

BC

[Plantbrain]

Yea, you gotta add that as long as the KH is not too low/zero part in there

I'd say it's(the method) rather consistent.
But a measurement and the cost associated with KH is not much trouble either.

The closer/more accurate a measurement is, the better you know what the CO2 level is. It does not take much error to throw the CO2 determination off 5-10ppm.

regards,
Tom Barr

[BFG]

Bclee, how long should we turn off the co2 supply before we actually take the ph measurement. I'm using an external co2 reactor and I have no idea how long the co2 supply in the reactor will last while I turn off the co2 supply.

[geoffrey]

NO!

1) Collect sample measured pH immediately.
2) Collect 2nd sample and let it stand then measured pH again.
3) The difference in pH between 1) and 2) should be 1.6~1.7 indicating about 20~30ppm.

[PeterGwee]

I seem to hear or see that the max pH of water with addition of baking soda is 8.2...If that is true, the assumption of 1.6-1.7 drop of pH from the initial pH to obtain 20-30ppm would not work. [] That is only if the 8.2 thingy is really true though..never try though. I still prefer the conventional way of doing things.

[bclee]

I think you might have confused that with CaCO3 which is relatively insoluble at pH>8.2.

Bicarbonate solution can go up to pH 11 (I think...). BTW, did you know that water KH=1 with CO2 almost completely driven out has pH>8? (Our taps can go above pH 8.0.)

The good thing about this method is that you do not have to worry about the inaccuracy of KH reading due to non-carbonate buffers.

BC

[PeterGwee]

Mmmmmm....interesting. Is the 1.6 - 1.7 drop really equal to 20-30ppm of CO2?

[bttay]

Is there a table or formula that I can refer to?
Like; x pH drop = y ppm CO2?

[BFG]

Bclee, I have measured my tank water ph and this is the result.

With co2-5.3
Without co2-5.6

Only a drop of .3 difference. I am using ADA Aquasoil Amazonia. What would my co2 measurement in ppm be? Would I need to increase more co2 into the tank? Measurement was taken 1hr b4 co2 supply is pumped into the tank and 1hr before it is switch off.

[PeterGwee]

BFG, ADA aquasoil tends to lower the KH substantially during the initial stages and usually it is lower than 1 or so which the pH/KH/CO2 relationship would breakdown. You would still need to make sure the KH stays above 1 and better still at 3 or above if you want to use the pH drop method. I have use the ADA aquasoil before and it is rather troublesome as the KH tends to drop real fast during the initial stages due to the peat and you would need to look at the KH real closely or you might end up killing your critters.

[vinz]

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On 9/21/2003 12:18:02 PM

Bclee, I have measured my tank water ph and this is the result.

With co2-5.3
Without co2-5.6

Only a drop of .3 difference. I am using ADA Aquasoil Amazonia. What would my co2 measurement in ppm be? Would I need to increase more co2 into the tank? Measurement was taken 1hr b4 co2 supply is pumped into the tank and 1hr before it is switch off.
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BFG, you cannot assume that at 1hr before the CO2 starts, the water contains only ambient CO2. The CO2 level might still be high. What you should do is put aside a sample of the water from the tank and aerate the sample for a day (being KS here). That should pretty much bring down the CO2 level down to ambient.

[vinz]

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On 9/11/2003 1:23:14 PM

Is there a table or formula that I can refer to?
Like; x pH drop = y ppm CO2?
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BTTay, Chuck Gadd's chart. The thing is we do not know at what water temperature and other assumptions is that chart based on.

[bclee]

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On 9/21/2003 12:18:02 PM

Bclee, I have measured my tank water ph and this is the result.

With co2-5.3
Without co2-5.6

Only a drop of .3 difference. I am using ADA Aquasoil Amazonia. What would my co2 measurement in ppm be? Would I need to increase more co2 into the tank? Measurement was taken 1hr b4 co2 supply is pumped into the tank and 1hr before it is switch off.
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IME, the water will still be quite rich in CO2 even after the CO2 has been switch off overnight. Surface area:volume ration is quite low. The water can retain quite a lot of CO2.

Try taking a small sample of water. You can shake it very vigourously and leave it in the open overnight or even 24 hours. Test the water again.

BC