Any ideas???

[Trippingpara]

My wife has a 45 gallon tank that has been up and running for about a year now. We came home the other day and noticed that a couple of the fish seemed rather lethargic. The rest were swimming around as normal. Sure enough, they started dying one by one. I immediately tested the water parameters (pH 7.4, Nitrite is .05, Nitrate is 2.5 and Ammonia is 0). There are no marks at all on the fish (gouramis, head and light tetras, pink hearts, and sailfin mollies). We have been doing daily water changes since then and they keep dying. We are now down to one sole (and very lonely!) tetra. There is a ton of aeration (two large air stones and a Rena Xp3 spray bar on the surface). We have not added anything new to the tank or done anything to the tank except our normal weekly maintenance. Unfortunately, my tanks are all used up with fry so I didn't have a hospital tank to put them in.

Any idea what caused this? The pH is extremely stable and always at 7.4 and the temp is stable at 76 degrees.

 

[fishkeeper25]

your nitrite should be 0,
do u put declorinator when u do water changes?
how many fish did u have in total?
where they sick by anychance,white spots on them?
i belive alot in to much oxigen and that could also be a reason.
how old is your tank,was it cycled?

 

[Trippingpara]

your nitrite should be 0,
do u put declorinator when u do water changes?
how many fish did u have in total?
where they sick by anychance,white spots on them?
i belive alot in to much oxigen and that could also be a reason.
how old is your tank,was it cycled?

I know the nitrite is higher than I like but I've never had fish die from a 0.5 reading before. I always use Prime after water changes. There were 10 fish (8 of them were 1" or less and the two gourami's were a little over 2"). There were no white spots, missing scales or any other sign of stress, illness or injury. The tank has been up and running in the same configuration for over a year (same bioload, same air stones and filter, etc.) The only change I made was adding the Rena to the tank over a month ago. It was running on an AC70 and I added the Rena (while keeping the AC70), but that was over a month ago.