Tank Full Of Dead Fish In The Space Of 6 Hours

[rossyboy]

Hi guys I need some advice, i've got a Lake Tanganikyan African cichlid setup with a variety of tanganikyan fish and a Bristlenose catfish in there too.

I went to bed at 3am last night, did all the usual stuff (ie fed fish as usual time, turned light off, etc) and when i got up at 9am all but 2 fish were dead.

They all had there mouths stuck open as if they'd been gasping. Now i'd assume this means they've suffocated and struggled to breathe, but I am just finding it difficult to work out HOW?

Last water change was a 10% change 3 days ago (as normal), i checked the water once they were dead and the readings were all good, ie ammonia, nitrate, nitrite etc etc and also temperature at the usual 26'c.

I've asked the guy in my LFS who is generally pretty good for advice/help and the only thing he could suggest was perhaps the water mains in my area may have had work recently and chemicals added which came from the water change.

I've managed to rescue a Brichardi and the Bristlenose is still going strong and everything looks fine now... just don't want this happening again because i've lost about £150 of fish and i'd raised them all from juv's too!

Thanks in advance!

 

[SharonCC]

Oh dear! That is terrible!!! Could something have gotten into the water...aerosol spray, air freshener, or anything of that nature?

 

[rossyboy]

Not that I can think of, my tanks got a full hood on top and it's never off for more than 5 minutes when i'm doing a water change and during that time I wouldn't have sprayed or anything

Just really gutted!

 

[Colin_T]

It’s unlikely to be the water change because that was several days before the incident. Also rift lake water is generally very hard and toxins like copper & other heavy metals are less of an issue in hard water.

The most likely scenario would be you had a power failure or there might have been some uneaten food left over from the feeding. This could have caused an ammonia spike and in the high PH of a Tanganyikan tank, even a slight trace of ammonia would be lethal to all or most of the inhabitants.

If your test kit didn’t pick up any ammonia this morning with all the dead fish in the tank, I would say the kit is faulty or out of date. When you lose a tank full of fish it usually takes a while for all the ammonia to be broken down into nitrate after the bodies have been removed. If there were still bodies in the tank, or they had just been removed, there should have been a really high ammonia reading.
The other option would be temperature. If the heater malfunctioned and the temp went over 30C that would kill them.

 

[rhostog]

Very sorry about your fish - you must be gutted.
You could try asking your water board whether they've done anything to the water recently. As ColinT says, it doesn't sound like that would be the cause as it was several days before, but you don't want to risk the fish you've got left.
Has anyone used any insecticide aerosols, plug-ins, air fresheners, etc. in or near the room? Anything sprayed in the air could find its way into the tank overnight - the hood doesn't seal out all air.
It must make it a lot harder that you don't know the cause - hope you get to the bottom of it.