IndyTim

Have had a 10 gal freshwater aquarium for about 3 months now, and have lost 1 platy and 2 danios in that time span. I am currently trying to revive my last danio in a one gallon tank on its own, as I thought I had lost him yesterday. Currently have 3 Harlequin Rasbora's that seem to be doing okay. Fish develop red around their gills and are inactive before passing on to that big fish tank in the sky. I do a 10% water change every week and a 25% every month. Use a master test kit and readings for nitrate, nitrite, and ammonia are at or near zero. Ph readings, however, are high at about 8.3. Water heater is set to 74 degrees and the tank is not exposed to direct sunlight, and hood light is on about 7 hours during the day, off at night. There seems to be a good deal of algae on the glass and in the gravel. I typically scrub the walls right before I do a water change. I feed the fish tropical flakes once daily and occasionally some dried bloodworms.
I have now lost half the fish since I started (this is my first aquarium), and I'm losing the thrill of having one (and so is my nine year old daughter, who is crushed every time we lose a fish). The fish seem to develop their sickness right after I do a water change (and yes, I do de-chlorinate the water and make sure it's at a similar temp to the tank).
Thanks for any help you can offer.

jsalemi

Red gills can be a sign of a couple of illnesses including ammonia poisoning, though if your ammonia is 0 that can probably be ruled out. You may have some kind of parasite in the tank that the water changes stir up.

You can find info on common diseases here: http://www.fishlore.com/Disease.htm -- check to see if your fish have any of the other symptoms described.

IndyTim

for the speedy reply. I actually had looked at that page before going to the forum and registering with the query. I don't see anything else on there that looks like the problem. I agree that ammonia seems most likely to cause the symptoms, but my readings are zero.