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Re: CO2 Measurements
>> There has been a number of posts lately about peat wreaking havoc with
>> the pH/kH/CO2 relationship. I saw a *huge* effect when adding a small bag
>> with about 200 ml of fine ground gardening sphagnum peat to my aquarium.
>> With everything else kept the same, including kH and the CO2 bubbling rate,
>> in less than two days the pH dropped from 6.4 - 6.6 to below 6.0 (the lower
>> limit of my test kit). The pH had been stable for several months before, only
>> occasionaly raising to the 6.8 - 7.0 range when the CO2 yeast is near
>> exhaustion (tap water has pH = 7.4). So in this case in particular the
>> introduction of peat in the water *did* break up the relationship.
>Did you measure alkalinity as well as pH? The acids in the peat could
>reduce the alkalinity without dissolving into the water. That would drop
>the pH but would not invalidate the pH-KH-CO2 relationship.
Yes, alkalinity stayed around 5.0 - 5.5 all the time. So did gH (about 9).
I think the amount of peat was too small to decrease gH by a significant
level, which was my original intent. The substrate has something in it that
slowly increases hardness and alkalinity in the water, and I was experimenting
with peat to try to control that tendency. With that small amount of peat I
observed an actual slight *increase* in kH from the tap water value 5.0 to
something like 5.5 in about two weeks, changing the peat in the bag every few
days or so. With no peat the hardness goes to about 6 in two weeks.
So, if I apply blindly the pH-KH-CO2 relationship, I would conclude that the
CO2 level in the tank raised from its usual ~ 40 ppm value to well above 100
ppm, which is obviously not true.