Thanks for the replies everyone. My test kit was not working. I hadn't realised it was two years out of date.
I bought a new test kit (Tetra 6 in 1 test strip) and it gave a chlorine reading of 0
My barb died. When I found it dead this morning its colourings were very pale and its gills were red. My other fish and shrimps are not having any problems. What might have been wrong with the barb that died?
How are you measuring the chlorine - and the other parameters?
I measured all the parameters with my old Tetra 6 in 1 test strip except the ammonia which was taken using a test tube test kit.
Which dechlorinators have you tried? With some brands you are not supposed to overdose, but others are OK.
My main ones are King British Safe Water and Interpet Bioactive Tapsafe. I only use one at a time. Which one I use depends on which shop I buy my dechlorinator from. I am normally careful about getting the right amount of tap safe but since I thought my tank had chlorine in it, I felt there was more risk to the fish from the chlorine than from using too much dechlorinator.
One thing that does concern me is your nitrate reading. It is almost impossible to have a reading of zero in a tank unless it is planted like a jungle, which is not really a good idea with a UG filter as the roots clog it up. What kind of tester are you using for that?
My old test kit was also giving a wrong nitrate reading. Todays test with the new kit gave me:
Nitrate 25 mg/l
Nitrite 0 mg/l
Chlorine 0 mg/l
My tank has a lot of java moss but no other plants