Hello again
I've been working a lot the last few days so I don't know if anyone is still following this thread, but I'll keep going just in case.
I finally got a response from the water company. They sent me test results for the last six months. There are over 50 parameters, some chemical and some microbiological. The sheet gives minimum, maximum and mean levels of each, plus the number of samples that were taken.
The results for chlorine were as follows
free chlorine max = 0.56 mg/l ave = 0.39 mg/l(from 68 samples)
total chlorine max = 0.64 mg/l ave = 0.45 mg/l (from 68 samples)
I think the dechlorinator I use should be able to cope with this. Not sure what other things in the water could be giving me the problems, but I have lots of information here if anyone has any suggestions.