Wouldn't the greater danger be that you could be developing a strain of fish which have a weakened immune system which would not be strong enough to keep the fish healthy without the assistance of a sterile environment? The other problem might be the development of mutations of the bacteria and viruses being exposed to the UV or ozone which are resistant to the UV and/or ozone. In either event, these are long-term to very, very long-term problems (how long would it take to develop a strain of fish with a deficient immune system). ------------------------------------------------------------------------- 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"!