I have never used substrate heating. Dupla recommends it strongly for planted tanks, and it is a part of their overall plant-growing regimen. I can follow Dr. Kadar's logic quite easily, and it is a probable explanation for the L&S recommendation. Unless you are having trouble, I wouldn't worry about it too much. Bob Dixon Cichlid Trader List Administrator ------------------------------------------------------------------------- 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"!