So as always dechlorinator MUST be used where water comes from the tap.
Not all dechlorinaters will break the amine to chlorine bond. If your water is disinfected with chloroamine your fish are still at risk when using most 'water safe' products and have spent money for nothing. The more the source water has been filtered through kidneys the more likely that chloroamine has been used. There many parts of the UK where I would not live. Water companies can be a little coy about the use of chloroamine, but the kidney count is a good indicator.
My tap water is from a small local supply (part of a very big water company, but the water is very local) and I can hear, if the wind is in the right direction, the warning sirens when chlorine is being added at the treatment works.
[Of topic, wife & I do have our own gas masks (WW II re-enacters) and yes I am aware of asbestos in some filters]