I can answer this question from first hand experience. i used to live in a northern New York town which had tap water with a hardness reading of 300 ppm. At that time I was mostly into angelfish and discus. At first I tried to solve the problem by mixing y tap water with rain water. That would have have worked if I coud have been able to collect enough rain water. Actually, I could in the summer, but not in the winter. We generally have snow from December to April and melting snow is too much work. So I bought an RO unit and mixed it back in with the tap water. I found that 3 parts RO to 1 part tap water would really work for the discus and angelfish. A bare bones unit can be bought from many different mail order places for $100-140 for a 24 gpd device. If you have hard water and like soft water fish, this is the best way to go IMHO. Now, I live in another northern New York town that has very soft water ( less than 15 ppm GH and KH). This enables me to use the water straight from the tap. I hope this helps. Joe Hildreth 15 Cedar Street Potsdam,NY 13676 ------------------------------------------------------------------------- This is the apistogramma mailing list, apisto@listbox.com. For instructions on how to subscribe or unsubscribe or get help, email apisto-request@listbox.com. Search http://altavista.digital.com for "Apistogramma Mailing List Archives"!