I wouldn't add water from the hot tap - has been sitting about in the boiler picking up allsorts of unwanted nasties + copper from the pipes for example.
You wouldn't drink the water from the hot tap so why would you ask your fish to live in it?
I always boil water from the cold tap in the kitchen which is our drinking water supply then mix with cold water from the same tap till the correct temp is reached.
then there is RO water - but I don't do that so you'll have to ask others or use the search.
what are the parameters of your tap water supply like? nitrates? ph?
ok - so you would
I wouldn't and "they" say we shouldn't
and I suppose somone will have had a goldfish that lived in the toilet and smoked 90 a day Capstan Full Strength and never had a day off work in her life..........
It depends if your hot water supply is heated with a water heater or boiler. Storage depends as well, if it's gravity fed from storage in the attic, it's generally a bad idea.
It's up to you in the end, but i've never had any problems and even had panda corys over a year so if it was bad it would of killed them, but i do use declorinator that removes heavy metals.