Sudden Fish Die-off

[carled]

...not a good day. I have a small community tropical tank. Bit of a newbie, but everything in there has been fit & healthy for 18 months. Recently lost one glowlight tetra and a zebra danio that I put down to old age basically. Two other glowlights and three other Danios were fine as always.

Got a few tiny new neon tetras and a couple of small black widow tetras on Saturday as special request from daughters. Also did half water change as normal. One Neon tetra died over the weekend, so my wife took it back to the shop yesterday and they replaced it and also gave us another black widow as one of the two they supplied uis with had a damaged gill cover. Wife put the black widow into the tank (after half an hour acclimatising in the bag) along with the water from the pet shop. Then she noticed that half the tail of the replacement neon tetra was missing so she took it back and got ANOTHER replacement, then put that in the tank along with the shop water... (not a good idea, I know, but I forgot to tell her not to put the shop water in the tank whilst I was at work).

She last checked the fish before going to school at about 3pm, then at 5:30pm looked again and found to her horror that half the fish, including my existing ones were dead or dying. By the time I got home and frantically fished the remaining fish out to put in a fresh bucket of treated water, we'd lost all 4 new neon tetras, one black widow, both full-grown glowlight tetras, a leopard & a zebra Danio and my two prized merino shrimps

I managed to save my two corys, one zebra Danio and two black widow tetras. I rinsed out the entire tank, filters, gravel & ornaments then refilled it all and put the remaining fish back in. Touch wood, they were all still alive this morning...

A water test on the "death tank" water showed slightly (but not amazingly) higher ammonia than normal and a very small amount of nitrite. Sod's law, I'd just run out of nitrate tester at the weekend and new test kit hasn't yet arrived, so no idea what that was. When the surviving fish got put into their emergency bucket home (along with the heater to keep them warm) the Danio looked really ill. He was on top of the water twitching and flitting about the tank, looking really agitated, curving his body and even jumping clean out of the water a few times. Over half an hour or so in the new clean water he settled down and after an hour or so, looked happy again and he (and all the other fish) happily took food when I put a few flakes in.

Basically the five surviving fish are now in what is to all intents and purposes a new tank... not ideal, but I have nothing else to put them in, so I just have to cross my fingers that they can put up with new-ish tank conditions while it re-establishes...

Anyone any ideas what could cause such a wipe-out in just a few hours?

 

[Miss Wiggle]

considering the fish you bought looked unwell they could have brought in a disease, there are some which will work through your fish that quickly.

it could also be related to your water change, you could have forgotten to dechlorinate (we all make mistakes, not blaming you just looking at possibilities) or it could be to do with the new water you put into the tank. Water from our taps fluctuates in quality i've heard a story before of someone missing a water change one week, then egtting a letter from the water company apologising as on the day they were meant to do it they had an accident and the water was contaminated with a massive amount of ammonia, had he done a water change he'd have easily killed all his fish, and depending on the concentration it could happen that fast. Also if the pH or something like that was different that day the shock could wipe your fish out. you say you do a 'half water change' do you mean you replace 50% of the tank water? personally i think you should do smaller and more regular water changes, if the parameters in your tank and tap water are different such a large water change could cause problems.

 

[carled]

Thanks. Fair points. Did dechlorinate as usual and added a bit of nutrafin cycle. I've been doing the weekly 50% change for 18 months now with no ill effects and I'd have thought that troublesome tap water would have shown up straight away, not 48 hours later? Like I say, it was (according to my wife) a case of all looking ok at 3pm then at 5:30pm half the fish were dead!

If it was disease-based, I'd have thought that it would have wiped out all of the fish? I have three of my original fish that have survived (two corys and a danio) and two of the "new" fish (black widow tetras) that all seem (touch wood) fine this morning...

Dunno... maybe the shop water was loaded with ammonia and it caused just enough of a spike to damage half my fish? No idea...

 

[Miss Wiggle]

it could have shown up immediately, could have taken some time, it really depends what the problem was and how concentrated, in all likeleyhood without a sample of water from that day you'll never know.

50% changes in themselves aren't a problem, but combined with dodgy tap water could wreak havoc, so to be on the safe side smaller more frequent changes can be better.

diseases won't nescessarily wipe out all inhabitants, i had a very nasty disease in a tank once from fish from a dodgy shop within about 3/4 days all my fish bar 1 died, nothing i did could treat or save them except for one who inexplicably just didn't get ill. Like human's, fish's immune systems will be slightly different so you can't expect them all to react exactly the same.

i don't buy the don't add any shop water to your tank thing..... how much water was in the bag, what 2/3 litres at most?? seriously even if it had a massive concentration of ammonia in that amount of water going into a full tank with a mature filter really shouldn't cause a problem.

have you ruled out the possibility of murder? a fish may have gone on the rampage and killed half the fish, even species that are normally peaceful you will get the occasional aggressor

 

[AndreaC]

We had a simular thing once where we had contamanated water from the tp. I never used to test the tap water until after that. Luckly we had a letter before I did a water change so kept checking tap water before doing a water change. So glad we had the letter 1st!!

Glad you managed to save some fish. Sorry about those you lost

 

[Amunet]

One of the new fish probably brought something nasty with it.
I think that's what happened to our tank when during a time of panic when trying to get one to get better.. I put it into the main tank.
Well that was a huge mistake b/c whatever had killed it also killed half of the tank inhabitants.
I would treat your tank with some sort of antibacterial med... Even if your fish seem to be doing fine now.. I'd still treat it just in case.

 

[LisaLQ]

PH shock doesn't kill that quick, it takes days for the fish's body to register the difference. Like someone else said, they probably brought in something nasty with them (maybe that strain of columnaris that kills within hours?).

 

[MHunt]

The high ammonia and nitrite was probably from the decomposing fish. It does sound like the new fish or the water they were in brought something with them. I've had two instances of additions bring nasty stuff with them, fancy goldfish bringing fish lice with them and platy's with fungus and whitespot which spread to and killed off many of many of my other tropical fish. I generally never add the water that the fish came in unless i can't net the fish easily from the bag or if I trust the lfs that the fish came from.

 

[dwarfgourami]

I would say the advice not to add the water from the fish bag has some relevance for ich, as that has a free-swimming stage where the parasites may be present in the water but not actually in the new fish. With bacterial infections I wouldn't have thought it would make so much difference as I would imagine the highest concentrations would be in the new fish and not in the water. The best solution of course is quarantine.

 

[vinylman]

It could be worth taking the trouble to find out which day your water company adds it's Chlorine and Chloramines to the water supply, then do your water change the day before.