Dead fish

[Adam duncan]

I have a 45 gallon planted tank with a penn place Cascade 1000 canister filter. The tank has been up and running for about four years now and was stocked with 15 cochus blue tetras, 6 peacock gudgeon and 1 electric blue ram. I do weekly water change of 20% with a monthly water change of about 40% as well as weekly tests using the api master kit. The tank is kept at 77.5°.


About a week ago I noticed that one of the tetras had dropsy. I added some aquarium salt to the tank and after a couple days of the dropsy worsing I removed the fish and placed it in my turtle tank. I do this since in my experience dropsy in such small fish is always fatal and in my opinion being eaten by a turtle is better than suffering a slow death. The next day I found another dead tetra and gudgeon. I did water test and found that I had a large nitrate spike. I did daily 20% water changes. After 3 days there was still a large amount of nitrate. I did a large water change of 60% and added some zeolite to the filter.

I woke up this morning to find all of my tetras dead and the rest near the surface gasping. I removed the fish and added them to my 75 gallon aquarium. I removed the dead fish and tested my water. All water parameters are perfect.

I'm at a complete loss as to what killed my fish. Can anyone give me some ideas.

 

[rlederer]

How much salt did you put in the tank?

 

[Adam duncan]

4 tablespoons

 

[rlederer]

Salt is typically not helpful in a typical freshwater tank. It can be useful in a treatment tank for parasites and dropsy at a high concentration for a few minutes, but not as a general additive. I’m guessing the salt killed the neons.

 

[Adam duncan]

Really? I've used before and I used it before several water changes. I just can't see how the salt used a week ago would kill off the majority of the tank. The only thing that I had done different was the zeolite the day prior.

 

[rlederer]

Oh, a week ago? Then salt is probably not the issue. But I stand by my statement that salt in a freshwater tank is not helpful. I looked up the research by professional fish breeders and they say salt in a freshwater tank has no use, although a little might not hurt. Maybe the zeolite? I don't know about that.