scavenger. The only thing I do to tap water as a rule is use dechlorinator.
If you have well water, you dont have chlorine and therefore, you dont even need that.
If you Dont have a well, You will have chlorine in the water, and I have seen chlorine in the water kill fish fast (granted, a sick fish, but still impressive)
Letting the water sit out in an open topped container for 24 hrs or so , especially with a bubbler in it will remove the chlorine from the water.
The other thing a town or city might add to your water is Chloramine ( ammonia And chlorine, somehow )
That Wont just gas off out of the water and you Do need to use Prime or a similar water conditioner to remove it.
There are tons of chemicals sold to add to tanks, most of these you dont need to worry about. Unless you have a special situation with special needs and expert advice, Id say stay away form other additives. clean water, good food, should keep the fish healthy.
PS BY THE WAY
NOT A STUPID QUESTION. some fish are tougher than others, but there are some things that No fish should be exposed to IMHO and that includes chlorine. keep the questions comin :thm: