Actually the distilled water should have VERY little CO2. The problem was more that likely from the distilled water having no hardness( KH or GH). It would take very little time for the CO2 and waste from the fish to trigger the acid fall. I had something similar to this happen with my Discus tank. If the fish are looking stressed try adding tiny amounts of Reef Builder. BRAD ------------------------------------------------------------------------- This is the apistogramma mailing list, apisto@majordomo.pobox.com. For instructions on how to subscribe or unsubscribe or get help, email apisto-request@majordomo.pobox.com. Search http://altavista.digital.com for "Apistogramma Mailing List Archives"!