It seems like a crime to go to all that trouble and expense to get RO water, then just go back and add tap water. Many people raise fish in pure RO water and this works great. Filter through some peat or add a bag of peat to lower the pH a bit and add tannic and humic acids and you really should be fine. If you must add buffers why not try products like RO Right and such. -Doug Brown debrown@kodak.com ------------------------------------------------------------------------- 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"!