Cichlid Tank Overheating Deaths?

[Pimelodus]

I have had a 60 gallon African cichlid tank running for the last five years.
Recently, the fish have been acting strange and I have lost two pictus cats, one ob peacock, and just today a pseudetropheus socolofi. Both of my adult male yellow labs have been swimming vertically in the tank, every so often darting to the surface or hitting the walls. The other socolofi are "shimmying" almost to the point where it looks like they are having a seizure. As I am watching now, they are acting like the labs where they dart sideways and run into the walls. Most of them are eating normally, but swim with clamped fins. All of these fish were fine for the past few months, but they all seem sickly now. My compressiceps seems to be the only cichlid left unaffected. Many of them are either swimming at the top of the tank, or wedged themselves into the rocks at the bottom.

I tested the water and found:
0 ppm ammonia
0 ppm nitrite
20 ppm nitrate
8.2 pH

When I checked my heater, it was heating the water to 86 degrees! I replaced it right away with a new one, and have been slowly moving the temperature back down to the target range of 78. Is this the reason why they're acting like this? I added an airstone in case there was a low oxygen problem.

Any help would be greatly appreciated, and let me know if you need more information.

 

[Circus]

That sounds like it could be it. Most fish don't do well over 82F. After the temperature stabilizes I would do a large water change.

 

[Colin_T]

Pictures and video of the fish?

86F is not going to cause that.

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When the temperature drops back to normal, do the following:

Wipe the inside of the glass down with a clean fish sponge.

Do a 75% water change and gravel clean the substrate every day for a week. The water changes and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use them. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens.

Increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.

 

[Pimelodus]

Pictures and video of the fish?

video of lab
video of lab swimming strangely

I'll try to get more videos later on

 

[Fishiemang]

At that temp you'll trigger mating stuff maybe, but certainly not deaths. That aint warm.enough to kill them fish. Especially happening gradually.

Since you added an.air stone, put the heater behind that. It will circulate the water past the heater and keep it at a more stable temp.

Your params.are.fine. Anything new added to the tank? Fish? Decor? Plants? Any heavy gravel vac before this started? There are several things that can cause the behavior and results you're describing...

 

[Pimelodus]

At that temp you'll trigger mating stuff maybe, but certainly not deaths. That aint warm.enough to kill them fish. Especially happening gradually.

Since you added an.air stone, put the heater behind that. It will circulate the water past the heater and keep it at a more stable temp.

Your params.are.fine. Anything new added to the tank? Fish? Decor? Plants? Any heavy gravel vac before this started? There are several things that can cause the behavior and results you're describing...

I added a new piece of dragon stone approx. two weeks before it happened. No new fish were added, and I didn't heavily vacuum the gravel recently.

 

[Fishiemang]

Did you boil it good before adding it? Clean it out good?