HELP - Great Tank Die-off

Actually, I like anonapersona's methodology. Good level-headed call.
good luck
:)
 
If there is no ammonia or nitrite reading, and the fish died of no desease symptom, then it appears to be toxis effect from some unknown source. Did you put anything new to the tank that could release toxin? I once placed some ornamentl sliver shining rock in my tank that I bought from rock shop. The fish kept dying for no reason, not right away in a one to several days. I kept replacing new fish and they kept dying. I lost many fish before I realized that one little piece of silver rock must be releasing heavy metal that killed my fish. Once removed and I did a large water fish, the fish stopped dying.
 
Autopsy?

Unless you have done a scraping of the fish that are alive and examined that under a microscope, and done a post-mortem on the dead, with full examinatin of internal organs, you can't just jump to "no disease".

Two weeks ago new fish were added. Now fish are dying right and left.

How were they added? Did any fish store water mix with tank water? Were there any dead fish in this store tank? What sort of procedures does this place use for new fish? Are they isolated in a tank all alone, just the new shipment, or are they dumped in with all the shipping water into a tank with the other fish of the same sort who have been there for weeks or months? If so, how would they know if there were any problems with these fish, vs the other older fish? Do dead fish stay in the tank long enough to be eaten? Do all the tanks share filtrations, so that what is in one tank is in each tank?

It is quite likely that these new fish had some bug of some sort that they were tolerant of, but the old fish had never been exposed to. Like small pox killing the Indians, it has decimated the tank.
 
Originally posted by Tiger15
If there is no ammonia or nitrite reading, and the fish died of no desease symptom, then it appears to be toxis effect from some unknown source. ......
Exactly.

My previous post is not at all that 'far fetched'.....
You may never find the toxin unless you have a positive test on the specific toxin.
 
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