Fish die unexpectedly after weeks in a tank

[jdz1001]

I have a 250 gallon saltwater tank set up with about 10 fish (large to small). This tank used to be an aggressive tank turned to a reef tank. All of these fish have been in the tank for more than 6 months. Nitrates are higher than they should be but has not been an issue before. Now when I add new fish they survive for weeks - they eat fine and no one visibly picks on them. All of a sudden the new fish will stop eating and be dead within a day with no visible stress spots or behavior . Anyone have any thoughts? All of the old fish have no issues.

 

[Jay Hemdal Verified Community Expert]

Welcome to Reef2Reef!

It may be that the issues with the new fish were not all closely related, some of them may have had different reasons why they died.

Moving fish to a new tank is always a very stressful period, with various risks coming into play; hitting the fish with the net, acclimation problems, then aggression problems from the original fish once they get into the tank. Most of those issues however resolve (one way or another) within a few days to a week.

You say the fish that died showed no symptoms? Did you see any rapid breathing? That is often missed by aquarists, but it is a sure sign of problems.

To possibly tell more, I would need to know the full list of fish in the tank and the list of fish that died, even then, it may not be possible to figure this out after the fact.

Jay

 

[mtraylor]

First to mind would be flukes that maybe you have missed heavy breathing. Would be better if you listed existing fish and new fish that had issues