Join Date: Jan 2008
This is quite puzzling, the reference solution should not be green.
If the reference solution is a 4 dkH reference solution, then it should either be clear (if nothing has been added to it) or blue (if the bromothymol blue is pre-mixed into it).
Perhaps you could mix a new reference solution up?
As for your other question (why the solution in the second bulb (the reference bulb) is not green anymore), it might just be the colour is getting hard to read due to aquarium lighting/plants, etc.
If you take out the drop checker and put it against a piece of white paper, is it easy to read?
If not, the only other thing I can think of is that the indicator (the bromothymol blue) is starting to break down.