What type of water do you use for magic fish?

"Magic fish" is a bit of an ambiguous term. Are you talking about:

* Fish that are used in magic tricks? If so, they are regular fish, and you would use the same type of water you would use for any other aquarium fish.

* Fish that have magical properties in a fictional story or game? Then the type of water would be dictated by the specific rules of that world.

Please provide more context so I can give you a more specific answer!