Are you using tap water? If so, have you had it checked for copper or iron? Depending on the pipes the water is going through it may have something leaching into the water.

That's what happened to me. I'm happy to say that my fish are doing fine since I am buying filtered well water from the LFS. I don't have to add a dechlor product and the ammonia, nitrite, and nitrate levels have been absolutely beautiful.

Go to your fish store and tell them you would like for them to test for copper and iron. They should give you a piece of foam which you throw in your tank and leave for two days. You then take it back to them. They can tell by the color that the foam becomes which if either of these two metals are present in your tap water.

Give that a try. Good luck,

Were the casualties fish which had been purchased? The reason I ask, with a Charles Harrison workshop on parasites freshly in mind, is that a lot of fish from the wild, from fish farms and even from other aquarist's tanks, seem to come with some parasite or parasites in their system. And when large parasites are effectively treated (as with Camallanus), if the fish can not shed the bodies, then the fish will die. And we may not know for up to three months that the fish are even infected! :(

Yesterday afternoon, we compared notes with some friends who had some Illinois fish from a quite polluted stream (someone had rolled a petroleum tanker upstream). I had similar problems with some Missouri fish taken from a small drainage ditch which had been a stream and marsh up until a bunch of construction the year before. In both cases, the habitats were pretty badly degraded and presumably that effected the fish's resistance to parasites. We quarantined the fish and treated them with a preventative treatment (from PetSmart) with Parziquantel and Levamisole - two anthelmintics which are effective against a lot of possible parasites - and the antibiotic Metronidazole. The product is called Gel-Tec Ultra Cure PX. As with Fluke-Tabs, it is pretty darn effective against a wide spectrum of wee beasties, though the antibiotic means that it should be used in a quarantine tank (bucket in our cases) so as not to trash a nitrogen cycle.

Both of our tanks were re-infected with anchor worms (which in 45 years in the hobby I've never had to deal with) because they lay eggs in the fish and elsewhere. It turns out that the eggs were not effected at all by the treatments!

Charles noted that fish do not just die for no reason. But the reasons may have had nothing to do with your excellent care.

Were there any tiny worms or critters sticking out of the anal vents, sides or gills? For more ideas of what to look for would you please look at my tag on list to Angelhologram's list in http://www.guppylog.com/story/2005/6/24/82111/0134

One can treat an established aquarium with an anthelmintic like Flubendazole, Levamisole or Parziquantel and except for messing up snails after a few days, can effect a lot of worms, crustaceans and even some flagellates (such as Hexamita) and protozoans. That can get expensive though. For one source see Charles' (the Inkmaker's) site at http://inkmkr.com/Fish/

Ten bucks will get you more of the FLUBENDAZOLE than you will likely need. Jehmco might be even cheaper, I don't know if they includes as detailed instructions. If you Google pond supply sites, they sell Parzi or something like that. That is Parziquantel. No one anthelmintic will treat everything though.

I would recommend sources like those. I went to our local vet and asked for a stock solution of Droncit (Parziquantel for dogs), slipped a digit in my formula and had them make up far more than I needed. Then it was a case of stiffing them or swallowing the three figure price myself. I wanted to stay cordial with them and though painful, it seemed the right thing (anyway) to pay for all of it. It was my gonzo math error.

The stock solution needs to be refrigerated. If it is freezing or too hot I don't think it will ship or I would offer some for postage. (If you were ever to swing through the Chicago area with a styro box, I'd send you home with a medicine vial and an ice bag separated by cardboard in the styro.)

I don't know if the possibility of parasites - external, gill (sort of external) or internal - will account for your losses. But they might.

A tiny pair of pygmy sunfish (Elassoma evergladei) followed me home this last weekend. They were bred and raised by a very skilled aquarist who is doing a lot of things I only wish I was doing with fish. Still...after I get them fully adjusted to the quarantine container and our profoundly different tap water, I will give them a preventative treatment with an anthelmintic or that Gel-Tec Ultra Cure PX (if I can borrow it back from the guy I lent it to). Until I began to see all of the grief (via Guppylog) that aquarists have had with parasites, I would never have bothered with that.