Soaking

[Eel Noob]

Try putting fishes in untreated tap waters and see what happens.

Tap water conditioners are relatively inexpensive and last forever.

[Kevin1]

I'd recommend getting a water conditioner that also removes hard metals because some of them(like copper) are deadly to frogs. It doesn't matter what species of frog it is, using untreated tap water is never ok to use.