Sorry but one pH drop in tank water equates to approximately 30ppm regardless of dkH your chart confirms this. Normal tank water will have about 3ppm CO2 from the atmosphere.
I am sorry for resurrecting an old thread but I really need help here.
I agree with the 10x progression, but where did you find this "3ppm CO2 from the atmosphere"?
I have been going through this over and over, and what I've found out is that our tanks should have around 0,55ppm of CO2 from the atmosphere.
I would love to be wrong and learn something...
I played around with Henry's Law, mostly with the solubility being defined via concentration, so that I can finally find it. That can be calculated using [CO2(aq)] = KH x pCO2
To calculate the CO2 partial pressure I considered that the air had 0,037% CO2 and temperature is 25C, and to be a bit precise, we discard the water vapour pressure by using this equation: pCO2 = (P° - pH2O) * XCO2
The result is:
pCO2 = (P° - pH2O) * XCO2
pCO2 = (1,0000 atm - 0,0313 atm) * 3,7 x 10-4
pCO2 = 3,69 x 10-4 atm
I dont think removing the water vapour is relevant, but I did anyways.
From there we proceed with the rest.
[CO2(aq)] = KH * pCO2
[CO2(aq)] = 3,38 x 10-2 * 3,69 x 10-4 mol x L-1 x atm-1 x atm
[CO2(aq)] = 1,25 x 10-5 mol x L-1
and then convert it to mg/l:
[CO2(aq)] = 1,25 x 10-5 * 44 x 103 mg x L-1
[CO2(aq)] = 0,55 mg x L-1
So, in the end I am looking at this 0,55ppm value and wondering, is that it, really?
A 1 point pH drop would add 5,5ppm. Considering that the water is not completely degassed from one day to the other, it would be possible to higher levels after a couple days.