I just looked at one of my tanks and the heater has been unplugged all night

All but two maybe three fish appear to be dead

The temp was 12 degrees. I did a warm water change and brought it up to 15

I have put some extra heaters in the tank too.

Is there anything else I can do to help my fish survive?

It was a growout tank for my young fish, it had 8 cockatoos, 2 angels, a bristlenose, a young pair of firemouths and a brown hap in it (tank is divided). the brown hap and the bristlenose are still swimming around, so should be ok. All the other fish are on their sides. One of the firemouths is still slowly breathing and moving his pectoral fin. one of the cockatoos is breathing too. None of the other fish have shown any sign of life yet

Plug the heater back in. That's all you can do.

And you probably don't want to warm it faster than over maybe 5-10 hours.

Oh, and I wouldn't flush the "dead" fish yet. You're not dead until you're warm and dead.

just let it come back up slowly, so it doesn't stress them out any more, and cross your fingers for the floaters

good luck

I know this from experience that bringing a tank up to temperature quickly will most likely harm if not kill the fish.

Best thing you can do is plug the heater back in and leave it.

the tank is now 23 degrees

The bristlenose and brown hap are fine

the male firemouth is swimming around on its side on the bottom, occasionally getting upright

Everything else is dead - 1 firemouth, 2 angels and 8 cockatoos (and 2 sets of wrigglers they had have died two)

Sorry to hear about your misfortune.

I learnt the hard way too and now all my tanks that contain valuable or favourite fish have 2 heaters in them. The first is the primary heater and the second is set slightly lower and only ever turns on during water changes, extra cold nights or primary heater failure. Cheap insurance I recon.

Gutted mate I am very sorry to hear about your losses But also glad to hear that some survived, keep a good eye on them over the next few days for whitespot etc as changes in temps can cause issues..