kH changes with CO2 injection

[reiverix]

I finally have my 20g just the way I want it with fish and plants. I have DIY CO2 and it's working fine. I've been monitoring my water readings every day for the last 3 weeks since I got my nitrates down from a stupidly high level. The CO2 has been running for two weeks.

What I'm a bit confused about is the way that my PH and kH are affected by the CO2. My usual PH is 7 and kH is around 3.5

When I added the CO2 injection my PH dropped to 6.7, which I was expecting. But my kH rises to over 4. If I remove the CO2 injection for a day, the PH goes back to 7 and the kH drops back down to 3.5.

Is this normal?

 

[djlen]

1/2 point fluctuation in kH is not unusual at all. There are a number of factors that can contribute to this. I rarely even check kH anymore.
The pH is affected because you are injecting carbonic acid into the water table, which causes a drop in pH. You really want to keep that injection as stable as possible with as little variation in pH as possible. Fluctuation stresses fish.
When you learn how long the bottle of mixture takes to exhaust itself, it's a good idea to make up a fresh bottle a day ahead of time and trade them off before the rise in pH starts. You'll grow the plants better and the fish will appreciate the continuity in parameters.

Len