Mysterious fish deaths in the tank! Help please.?

Question

The fish have been fine, until.. the filter broke down on sunday. I put a new one in. Tuesday night two mysterious fish deaths, no change in colour, cotton mouth/wool or cloudy eyes. Wednesday another death. All the same species of fish. The neon's are fine as are the plec's. The water was tested today (before the 3rd mysterious death) all levels are fine. Why is this happening? Any advice would really help please.

Answer 1

When you changed the filter, did you use the old filter media or did you put a brand new one in? If you put a new one in, you lost all the good bacteria that was built up on the old one, which can cause a mini (or full) cycle in your tank, and can cause fish deaths.



Test your water and see if you had an ammonia or nitrite spike, and do a water change.



When I replace a filter, I usually either try to get the same brand I had before (if I liked it) so that I can use some of the old filter media, or I put the old media in the tank while the new one is running, until i am sure (a few weeks at least) that the bacteria has had a chance to begin growing in the new filter.



Good luck.

Answer 2

I suspect the water parameters are not fine.



If the fitler was completely replaced then the new filter will not be cycled and ammonia/nitrite will be building up in the tank.



It may also be toxins released from the failed filter. When the filter fails the media may become anoxic (no oxygen) and produce some pretty nasty stuff.



I suggest you may need to do some large partial water changes to bring the levels down. I would do that anyway, something is wrong with the water, best way to fix that is to start changing some of it.



From personal experience, when you get unexplained fish deaths.. start changing the water and they stop.



Ian

Answer 3

What type of fish died? When you replaced your filter, did you save the old filter media containing your beneficial bacteria? Did you add any new fish when you replaced the filter? It's very possible that ammonia is spiking in your tank, or that the pH fluctuated too rapidly if you did any water changes. Also, it's possible that the flow of the new filter caused a rapid change in the tank temperature which shocked your fish.



Knowing what type of fish died will help in obtaining better and more specific answers. Also, what was your old filter and what kind is the new? Did you rinse the new filter, or just plug it in?

Answer 4

What kind of fish are they?

What size is the tank?

How many fish are in the tank all together?

Did they act strange or show any signs?

How long has the tank been running?

Was it cycled?



It could be any number of things, you'll have to answer those questions first to get an accurate answer.

Answer 5

Did your old filtration have Bio wheels? If so did you change them? If you did have Bio wheels in then dont change them. Then only other thing I can think of is some type of chemical in the new filtration system. You may just have to let it runs its course.