Fish Kill - Advice Needed

[denverjon]

I just lost 20 of my 25 fish and I'm completely stumped as to the cause. Three weeks ago, I upgraded to a 210g and lost one fish during the move. Everything looked good and was eating well with no sign of ich or other disease. I left town for the weekend and when I returned two days later most everything was dead. For what it's worth all of my corals (sps and lps) are doing great.

I was thinking the cause might be high ammonia or nitrates but I had my water tested and the ammonia levels were 0 and Nitrate was 2. Nitrite was .021. My copper levels were a tad high at .04 but I don't think that's enough to kill fish. My salility is fine and water temperature stable so I can't figure out what happened.

Any thoughts?

 

[swannyson7]

pH or temp fluctuation? Do you have a controller to look back at a history of your parameters over the past few days?

 

[denverjon]

I do have a controller but can't look back. I did keep my lights off for the better part of 72 hours. I wonder if the water temp could have gotten too cold? I keep my temp at around 80 degrees and I don't know how much it could have dropped. At what temp would fish start dying?

 

[clowndude]

I would have taken one of the dead fish to your LFS to check for a disease. Also did u have anybody feeding your tank while u were gone? I'm wondering it the co2 levels climbed in your tank, especially since u left the lights off meaning everything is giving off co2.