Established tank - sudden deaths - does this happen to all of us?

[dmaccy]

Hi
Long time since I last posted but habe always found advice on here helpful. Not sure if it's advice this time or reassurance.

It took me a while to get there but i have a well established 240 litre tank with a healthy mix of rasboras, tetras and corydoras.

However in the last 48 hours I have lost 12 fish! Obviously I'm now doing everything to save as many fish as possible. There is no obvious signs of any abnormality.

But wondered how often this happens in an established tank and does it happen to the best of us?

The most likely cause by the way is either the gravel I topped up a couple of weeks ago (although the impact would have been delayed) or new fish added last week.

Not necessarily looking for advice on how to rescue the tank but more from others to tell me this can happen to anyone and all we can do is make the risk of it as low as possible.

 

[MattW]

I haven't had this happen to me yet but I have seen other posts on this sort of issue. Parameters could have changed, a checkup on them would be a good idea. Do you use tap water? Perhaps works on the water pipes were done in surrounding areas so something could have been introduced into the water through WCs? I've heard horror stories of that happening and decimating tanks before.

Out of the two things you mentioned the new fish would be the more likely cause IMO. Perhaps they were carrying something that was harmful. Although most fish stores do treat fish through quarantine. Was it a chain store or a LFS you got them from?

Hopefully the situation improves

 

[Naughts]

or new fish added last week.

If you don't quarantine, this will be the problem. Post pictures of the remaining fish to try and identify any symptoms. Do large daily water changes for now, this will dilute the pathogen.
I haven't had a mass die off, I quarantine new fish for 4 weeks+.

 

[Back in the fold]

Yes , this does happen to every single one of us at times . All you can do is cast a critical eye on everything and do your utmost to find the cause . There is a phenomenon called “ sudden unexplained fish death “ and it is most commonly just one fish that had been healthy for a long time but I see no reason it could not also apply to several fish at once . You are absolutely right when you say that this can happen to anyone and all we can do is make the risk of it as low as possible . You have had your turn and you have learned something . Be glad it’s now behind you .

 

[Colin_T]

You water quality has gone bad for some reason (usually changing filter media/ materials).

The fish you bought a week ago probably introduced something that has started killing now.

You did something to the tank yesterday and it poisoned the tank.

You had visitors yesterday and someone put something in the tank and that has poisoned the fish.

Post pictures of the fish (dead and alive) so we can check them for diseases. If they have something wrong you could lose the entire tank.

 

[Colin_T]

FIRST AID FOR FISH
Test the water for ammonia, nitrite, nitrate and pH. Post results in numbers.

Wipe the inside of the glass down with a clean fish sponge. This removes the biofilm on the glass and the biofilm will contain lots of harmful bacteria, fungus, protozoans and various other microscopic life forms.

Do a 75% water change and gravel clean the substrate every day for a week or until the problem is identified. 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. It also removes a lot of the gunk and this means any medication can work on treating the fish instead of being wasted killing the pathogens in the gunk.
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 the media. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens so any medication (if needed) will work more effectively on the fish.

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

Post clear pictures and video of the fish so we can check them for diseases.
You can upload videos to YouTube, then copy & paste the link here.
If you use a mobile phone to film the fish, hold the phone horizontally (landscape mode) so the footage fills the entire screen and doesn't have black bars on either end.

 

[GaryE]

It happens when we add unquarantined fish that can be carrying viruses or bacterial infections. Sometimes, they don't get sick, as carriers. But with the losses you've had, that's suspect number one.

If, like most people, you've gotten complacent about water quality and dropped off a weekly water change routine, that will do it too.

Plain old mystery die offs happen. They're mysterious because we can't see the causes, just as covid would have been blamed on demons back in the day. I've had sudden disease breakouts that hit one species or one tank, killed and then settled down. There are always reasons, but we don't have labs or tools to read what we see, and can only guess.

When it happens, it's really frustrating. When I see anything go off, I immediately start on water changes every couple of days - 40% minimum.

 

[CassCats]

It happens, as Gary says.

Sometimes you won't get an answer, but I'd definitely suspect the new fish carrying something and wiping everything out.


One time, one of my established tanks, no problems with it, and woke up and all of my schultzei cories were dead. Just them. Nothing physically wrong with them and all of them were normal the day before. The sterbai cories in the same tank totally fine. Lost no other fish in that tank and only that specific species died. To this day I cannot understand why

Sometimes these things can happen inexplicably, many times though there is an actual answer if we have the means to find it.



Our tanks are closed systems, and when we introduce something from another closed system, it's possible it has bacteria or other pathogens that it was immune to in its previous system but the new system doesn't have that particular pathogen so the resident fish aren't immune to it and drop like flies. You may grasp at ideas, but without a lab you aren't going to know the specific pathogen, especially without outward symptoms.

 

[dmaccy]

I THINK I'm back on top of this now. I have no idea what caused it. Water parameters were consistent throughout (pH 6.8, ammonia 0, 6-7dGH , 1.5dKH, temp 25°C).
Alternate days 50% water changes and filter sponge wringing out.
Also did a deep filter clean too.

Only slight exception was an ammonia reading of 0.2 which came after the last death. So I'm hypothesising this was caused by the number of dead fish given I can't watch my tank 24/7.

Oddly the x ray tetras, juli cory, albino bronze cory and dwarf ottos were completely unaffected and my range of v. small rabsoras were virtually wiped out. I lost 4 of my 6 smudge spot cory in the space of 6 hours, the other 2 unaffected

I guess it's one of those things and we will probably never know for certain what happened.

 

[GaryE]

This is all guesswork, but we know species control some pathogens. It is certainly the case with tb, which fish can carry for years before it blossoms and kills. I see no reason why there shouldn't be other pathogens that can sit dormant in fish since long before you got them, either from nature, the farm or the store.

When a new stressor arrives, the pathogen can break out. It may spread if the dead fish are scavenged, but may not otherwise. Or if it does, it may settle in for a long dormancy while we happily think it's gone.

I've had single species die offs on the same day across 3 tanks. That makes no sense if you blame everything on what your test kit can read. But if the species carried a disease and all faced a mystery stress, it's sensible.

I've even seen generational die-offs in single tanks - where a bunch of 4 or 5 year old fish from the same purchase will keel over all at once, but their young will seem completely unbothered.

 

[Magnum Man]

I’ve had it happen a few times with the dominant of species, no fighting witnessed, and no other losses for months… I admit I don’t like losing the best, healthiest looking fish… but it does occasionally happen