Look up Neon Tetra Disease. I think that might have been imported from the additions to the tank. There's no cure that I know of and your best bet is to see who the survivors are at the end of this.
Another possibility is the sudden increase in bioload gave an ammonia spike, but by your readings everything is in the green. I'm sorry for your losses.
Maybe you should check with Blinky. She had a similar problem a couple weeks ago. It may be some sort of bacterial infection. She read about it and ended up having to sanitize the whole tank. Did you sanitize the new tank before you set it up? It sounds like it could be introduced either by the new fish or by the new tank.
Usually you can spot Neon Tetra Disease (NTD) as the fish lose color before dying. They start turning white where their muscles are infected with the parasite. As the previous poster said there is no known cure and survivors still carry the disease. However, there are other diseases that mimick NTD and are treatable, the only way to know for sure is in a laboratory. If it is NTD the only thing to do is quarentine survivors as they can pass on the disease.
I am doubting the test supplies. You went from media that was biologically sufficient to handle a load of four animals. You then added 6 more animals all at once? Biological filters only grow to handle the size of the bioload in a tank. If you have a wellplanted tank and suddenly take out all of your plants, expect ammonia and nitrites to spike. If you more than double the tank occupants of a tank, expect ammonia and nitrites to spike. That's why after a fishy cycle so many people advise you to add one or two fish at a time every two weeks. This should give a chance for the biofilter to catch up without too bad of spikes.
I also agree that without quarantine you majorly endanger the lives of your animals. I'm sorry you had to learn that lesson like this. I also would be shocked if those ammonia and nitrite readngs were correct. They simply couldn't be unless you added extra seeded media to the tank.
I've only had time to read half the replys, sorry, but my guess would be that when you added the new water to the tank, it was the same temperature, but you said you dechlorinated AFTER it was added to the 10g? the chlorine may have killed your bacteria (I always let my new water sit for 2 days with dechlor in it, and then heat it before adding it with an extra heater.) and your test kit isn't picking up the results.
sorry for your losses
I'm so sorry, it sounds like you are very conscientous and do everything you can think of. However, I agree with Harlock. You may have overpowered your bio-filter. Also, do you ware gloves when you have your hands in your tank? It wouldn't take much soap or lotion to kill your fish. We take such precautions with everything else, we shouldn't chance this either. Arm-length rubber gloves at BigAls are $15.00 and one less thing to worry about.
Thank you all for your replies. I do believe I have a raging case of Neon Tetra Disease going on here. :sad I never heard of such a thing, but my fish were definitely showing all the symptoms. I can recall that one neon, his colors got very weird before he died. I remember thinking that it looked like he was "short circuiting" in his red and blue stripes. I just euthanized my guppy too. I read that there was no cure and the best thing to do it get everyone out of the tank asap that appears infected. I am going to leave the tank alone for a while to see if the last neon makes it. The frog and loaches are still doing fine as well. One site I read said I need to wait 6 MONTHS before adding any other tetras! Could that be correct??
Also, for what it's worth, I still do not believe I had an ammonia or nitrite spike, or other water quality issue. I will be taking a sample of my water to the lfs next time I go, to test my readings against theirs, just to be sure. Yes, I did bring home 6 fish, but one died immediately and the others started dropping off within 2 days. I started doing 30% daily water changes when they started dying too. So I still don't feel that my test results were incorrect, but I will have the lfs test my water to be sure. I do not use gloves when I work in my tanks, but I am very careful about washing in plain water and not using lotion or perfume on tank maintenance days and I even have a nail brush to scrub under my nails before I put my hands it.
It is also true that I didn't use a quarantine tank, and I never have in all the years that I've been keeping fish. I have learned a hard lesson lately with the pictus cats bringing ich to my big tank (successfully treated with no losses, thank God) and now these neons bringing in their NTD. I plan to avoid impulse buys at petsmart or the other poor lfs near to me. I'll wait to go to the really quality lfs up north if I ever want to buy any more fish...
If it is NTD the only thing to do is quarentine survivors as they can pass on the disease.
