How about using Kent Ph minus. It comes as a powder which when added water produces (dilute?) sulphuric acid. I've bought some recently but have not fully tested it yet. A pH test shows about pH 4 can be obtained, don't know if it will be stable though. Ken. ***************************** Ken Laidlaw UK Astronomy Technology Centre Royal Observatory, Edinburgh Web: http://www.roe.ac.uk ***************************** ------------------------------------------------------------------------- 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"!