Water chemistry problem after CO2 injection

[PeterGwee]

Hi guys, had some problem now with planted tank. Initially my pH and KH were 7.2 and 3 respectively. But after a few days when i measured the KH, the levels shoot up to 7!!!! Vinz i think told me that there might be crush corals inside the substrate..okay i agree.. But now, the pH which usually rises to above 7.1-7.3 a couple of hours after CO2 injection and lights were off did not happen today. I began to take measurements and to my surprise the pH was 6.9 (pH test pen calibrated so was sure it was the correct value) and KH was 7?? How could CO2 levels be so high even after 3-4 hours of stoppage of CO2 injection? Please help me!!! I really don't know how to determine the safety level of CO2 anymore so as not to harm my fishes as well as to keep my plants growing well.

[vinz]

I wasn't the one who told you about the crushed corals. []

The reason we push the KH up to 4 to 6 is to buffer the pH swings caused by the amount of CO2 dissolved in the water. I.e. it reduces the amount of pH change when you start/stop CO2. At 7 KH, your tank is very well buffered, so don't worry about the pH level after the CO2 stops... you should think about getting your pH correct when CO2 is on.

Assuming that your KH will remain at 7, you need to adjust your CO2 bubble rate to get your pH to your desired level during CO2 injection. According to the chart at Chuck Gadd's site, you should probably aim for a pH of 6.9 to 7 to stay within safe CO2 levels. Measure your pH a few after your CO2 starts, then adjust your CO2 bubbling rate up to lower pH or vice versa.

Okie dokie? []

[PeterGwee]

Vinz Dokie okay []