Overdosing CO2?

Ian H

Guru Class Expert
Jan 24, 2005
Shipley, West Yorkshire, UK
I've just got an API KH test kit and used it to test my temporary hardness..........The result was 10 degrees. This was a bit of a shock as my KH is normally much lower. I re-tested with my Interpet kit and got a value of 5.

I tested my tapwater and got 3 on the API and 1.5 (on a 10cc/2 basis) on the Interpet. It's quite soft water here. I decided to add 1tsp of bicarb to 17.2 litres of tapwater which I estimated should give me 13 degrees in total on the API test, ( I based my calculations on a value of 1.1tsp in 50 US gals giving 1 degree hardness) Could you check my figures here please Tom or Greg?

I got a result of 15 (API) and 8 (Interpet). I considered the API to be the more accurate.

This has left me with a bit of a problem as my PH is between 6.6 and 6.8 and a calculated CO2 level of between 48 and 75 ppm..too high. I've reduced the bubble count to 1 every 2 secs and intend to do a 25% water change to reduce the carbonate levels. By the way the fish are OK.

Just a warning to all I suppose, my CO2 strategy was based on a KH result that was wildly inaccurate.