Sudden Death / What to do next?

[Ianb262]

I am very sad because of the passing of my 2 spotted puffers last night . I believe they died because of too much ammonia in the water (about 0.50ppm). I do not want to take down my tank so I was wondering how I can make sure my aquarium is ready for new fish. Here are the other levels of the water:

Salinity: 1.005
Ammonia: 0.25 (did a water change the night before, the fish were acting odd)
Nitrites: 0ppm
Nitrates: 25ppm

Thanks for any suggestions you might have to offer.

 

[Mr. Bones]

Massive water change, then try to find the source of all that nitrate. Most likely over feeding, plus test your tap water, or where ever you get your top off water or replacement water from.

 

[Mrscmurray]

Hi, did you cycle your tank before adding the fish? If not this could be the cause of the ammonia with the filter not having the capability to process it yet.

 

[Ianb262]

Hi, did you cycle your tank before adding the fish? If not this could be the cause of the ammonia with the filter not having the capability to process it yet.

Yes, I used SafeStart.

 

[Mrscmurray]

Yes, I used SafeStart.

How long was the tank running after this? Did you dose it in any way with ammonia or food and test the water at all?
Also do you know what your tap water tests at for nitrate before being added to the tank?