This is my first time testing for CO2 in my fresh water tank.
its a 180Gallon tank with a few tetras in it. The Salifert test kit
shows that I had to use 15 drops before the test water turned blue.
From what I read 1 drop = 5mg/L or PPM CO2. Was my test water suppose
to change to blue after 4 or 5 drops rather then 15?

My fish look fine, swimming on or near the bottom, plants are
producing oxygen bubbles, so not sure if I am reading this wrong.

any help on this would be appreciated.

James