Sorry Mike. We disagree, apparently vehemently. Not using an RO/DI filter (especially considering how inexpensive they are these days) is only asking for algae problems, regardless of whether the aquarium is reef or fowlr. I can't even think of one scenario that would warrant recommending to someone NOT to get an RO/DI. If you could possibly enlighten me, that would be greatly appreciated.marrone said:No that's not the case, since he from NYC the water is actually pretty good and if the tank is only going to have fish the water will be fine. There isn't a need to use RO/DI or even RO water.