You could also use distilled for evaporation. It is a bit more, but grocery stores carry it so if you can't get the ro
water from the fish store, there you go. Also if it is just Ro
water, it contains some level of contaminants, that is where the DI
comes in to get rid of the rest. A basic 5 stage RO
filter will pay for itself and can be put in a basement or under a sink in a cabinet. It pays for itself.