Hello all, I currently set up a 55 gallon that is going to be FOWLR. And the water is evaporating. This isnot my tank but my stepfathers, he wants to use rainwater to top off the tank instead of what i do and go to the pet store and get soem RO water. Should he do this. ( I have a 20 gallon tank which i only use RO water to top off). More over thefish that will be i nteh 55 gallon will all be from the wild, since we can catch some pretty angelfish down here in miami.