Sorry Aquadream, pH fluctuations do depend on KH. <br /><br />As an illustration, a 20 PPM increase in Co2 may lower the pH by 0.8 in low KH water, while the same in increase in Co2 may only lower the pH by 0.1 in high KH water. <br /><br />The fish don't mind the pH change as such, as it is not...