I've just re-joined the list so forgive me if I go over old ground. In my experience D.filamentosus are not agressive fish. My friend bred them in a very small tank and the male was never hard on the single female. They certainly would not harm the barbels of Corydoras, I'd go with the bacteria in the substrate or sharp gravel. The best substrate for Corys is definately sand - like Apistos they like to sieve it through their gill openings. Ken. ps - they are not easy to breed. My friend used deionised water with a pH of ~5.5 ***************************** 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"!