Thanks everyone for your input. I think everyone just confirmed my suspicion. It's not as straight forward as 50% RO 50% well. I'll mess with it to get the readings I need and go from there. Thanks again, Walt ------------------------------------------------------------------------- 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"!