Aquaponics - Sick fish

I had another fish die this afternoon, and one is in my kitchen in an aerated slightly salted bath, trying to get cured.

It has some fin damage to it's tail and, it has what appears to be mould on its back.

All the water tests report normal, so I'm researching all I can on fish disease. Actually there was a slight spike in nitrites (.25) but I think that was due to the dead fish.

Busy - what I need is a fish expert.

[edit from the future - All these woes ended up being part of an ongoing problem with me poisoning my fish with rainwater run off from a common garden plant which is highly toxic to fish - http://120thingsin20years.blogspot.com/2010/07/aquaponics-poison-plant.html]