Thanks to everyone who helped me with this issue. I have suspected the city water supply and the substrate might be culprits, but have avoided tearing down the tank because it looks so great right now. Perhaps I'll just try a different substrate next time. Maybe straight Fluorite topped with gravel next time. I'm curious to know whether the 'Purity on Tap MM80' is an affordable tap water purifier or one of the big bucks RO units. Is it possible to find something worth getting for under $100? Way back, I had a 20 gallon with that general type of substrate. I also had the same basic fish symptoms, although I had sudden deaths too. Test kits gave me nothing, but when I tore down the tank, the unaffected fish never developed any rot. Gary From: Helen Burns I would tend to agree with Michael on this - check your tap water. Three years ago in my fish house I had a similar problem with one species only, Satanoperca pappaterra. After a water change the dorsal fin would be left with only the spines. The local authority was obviously adding something 'extra' into the water system. I bought a 'Purity on Tap MM80' unit which removes all the nasties from the tap water. Since the day this unit was installed the Pappaterra never had this recurring problem. Helen Michael Grey wrote: >>Your water probably is treated with chloramine, a heavy form of ammonium and chlorine, and your current water treatment may not be neutralizing the chloramine. Check ammonia levels in your tap and tank. << ------------------------------------------------------------------------- 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"!