Help, 26 out of 30 fish have died overnight

[oscarsrock]

Hi everybody,
am desperate for help. Have 6ft tank for 3 years, Eheim fitler regularly cleaned, gravel cleaned fortnightly, OK not so great on water changes but 20 litres added each week with topups for evaporation. Everything was going swimmingly then fish got listless, off food, then started to die. Some had what looked like finrot and others a white fuzz on them. Lost 3 large silver dollars, 15cm Silver Shark, Giant Headstander, 18cm Yellow Severum,and numerous others. Only Giant Oscar, 1 Large Kissing Gourami and small Gourami still alive. Panicked yesterday and put them in small 2ft tank, added blue treatment and small amount of salt. Not looking good. Oscar motionless but still alive and fuzz seems to be clearing off slowly.
Big tank is drained and empty. If any fish survive what do I do with the tank to make it safe again. Any ideas what I did to cause this, no new food, no new fish, immaculately clean water, I am at a loss. Please advise.
Thanks

 

[dwarfgourami]

How many gallons was your tank? Water stats- ammonia, nitrites, nitrates? What did you have in it? Any chance that something could have knocked out your filter?

 

[ncjharris]

Fuzz could indicate columnaris, one of the side effects could be a weaken immune system and then fin rot. There are some good posts on this disease elsewhere on the forum - do a search and see what you get.

As DG said, giving us a bit more information about the state of your tank would help. When did you add your latest fish too; could be a chance they carried something into your tank and it infected all your livestock.

 

[CFC]

I think what we are seeing here is a form of"old tank syndrome", this quote

Eheim fitler regularly cleaned, gravel cleaned fortnightly, OK not so great on water changes but 20 litres added each week with topups for evaporation

is what leads me to believe this but some water tests will need to be done to confirm this.

Let me explain some more.

When water evapourates it is only the pure H20 which leaves the system leaving behind all the minerals, when the tank is topped up with tapwater the H20 is replaced along with another dose of all the minerals, then that H20 evapourates and another dose with all the minerals are added. Eventually over time the balance of minerals becomes too heavy and the water becomes no longer fit for fish to live in, their immune systems become compromised and they fall ill.

Usually regular water changes prevent this and the other form of "old tank syndrome" where the pH crashes overnight by removing old water and replacing it with fresh so that the balance of minerals stay true for longer, in marine systems where no water changes are done top ups for evapouration are done using pure H20 either from a R/O unit or distilled water so as not to tamper with the water chemistry.

 

[Gourami Girl]

This does sound strange.

Is it an external Eheim? As the tank is a large one with many large inhabitants.

If you're cleaning it every 2 weeks, this would surely incorporate the water changes anyway, meaning you were keeping up with them too?

most likely is a problem with the filter, perhaps someone switched it off for a time by mistake?

Do you have any stats?

Did you do anything differently? Was the heater accidentally switched off? Did the fish get spooked by anything?

Actually, reading your post again it sounds like quite a full tank, perhaps it simply got overloaded with the constant growth of the fish?

i'm not sure that draining the tank was a good idea, as now you will have to start from scratch. The most important thing is to fill up the tank ASAP and dechlorinate, add plenty of live bacteria to start the filter off.

As for the fish, treat them with Products for fungus and finrot, you may have to treat the illnesses seperately though. Use Waterlife products as they are very good. Reintroduce the fish into the large tank one by one, leaving a couple of days between each.

I would run the tank for at least a week though, as long as you can, before putting anyone back in.

good luck.

 

[RandomWiktor]

White fluff + raggy fins often = columnaris, especially when combined with rapid, massive die-offs. Did any of the fish have ulcerations under the fluff? By the same stretch, was it mostly on the head and gills?

 

[oscarsrock]

Thanks for you ideas. Last fish died yesterday, in small tank. Large tank is empty and dry (thought the air might be good for it, and I am a little shattered)
Filter and heater were both on and working perfectly. Will wait a while before setting up again. Tank holds around 300 litres and there were only seven quite large fish, the rest were Gouramis and a couple of little sharks and catfish.
If I refill should I leave the tank operating empty for a while?

 

[Gourami Girl]

Keep the tank running for as long as possible, now that you have no fish to house quickly, i would run it for at least 3 weeks, dechlorinate the the water, i would remove the gravel and rinse it thoroughly and i would also give the filter a good clean as it could be harbouring disease. Keep adding plenty of bacteria to the empty tank, keep the heater switched on and add a small pinch of food every 5th day, to help the bacteria start off.

I don't know what fish you are hoping to keep, but the general rule is add a few at a time, no more than four small ones, then leave it for 5-7 days, before addinf the next few. Dont, whatever you do, be tempted to add loads at once as you will almost definitely fall prey to new tank syndrome. Better to start off with ones that like hard water, as this will be what yours is, until it matures a bit more.

Then 10% water changes every 2-4 weeks, depending on inhabitants, don't forget to vacuum the gravel at the same time and clean the filter in the decanted tank water, to preserve the good bacteria.

GOOD LUCK!

 

[RandomWiktor]

I would sterilize that tank before I even thought of starting it back up; it sounds like you had a very pernicious disease going on in there. You could fill it with diluted bleach-water, but for bleach to work, it must be left to sit for at least 20 min, and who knows how long diluted? I also worry about bleach because I'd be afriad that no matter how many times I rise it, it'll somehow find a way to leave residue and kill my fish. However, I don't think boiling and salting a 6ft tank is feasable. Heck, bleaching and rinsing might not be.

Very sorry to hear about your loss =(

 

[cyprinut]

Sorry to read about the losses. I think CFC is on the right track on the cause. Major ph crash most likely the culprit IMO.