Backyard Aquaponics
A place to discuss aquaponics

I am having fish die and I have no idea why. I have about a 20 gallon tank with 3 goldfish and 4 koi, they are all roughly the same size (about 3-4 inches). Over the past week 3 of the koi have died, and I suspect the 4th may not last long. We didn't notice any odd behavior on the first 3, the 4th one looks like it is having a hard time staying down, it is swimming around at the top but isn't straight up and down like they normally are.

The goldfish don't seem to be acting any different, this system has been stable for months, all the tests for the water are very normal, its indoors so no temp changes. The only change I have made lately was I added a mint plant that is growing right out of the fish tank, I have it floating on a styrofoam raft with the roots dangling down in the water. I can't remember if the first fish died before I added that or not, but they were close to the same time.

I looked over all the fish that died and I don't see any odd colorations, nothing that would indicate they were sick. I am really stumped and feeling sick over losing these fish.

What should I look for? There must be a reason 3 of these would die all of a sudden, I haven't lost a fish since December up until now.

Help!!!

Humm... definitely something wrong if your Koi are croaking it...

Full range of water parameter tests please... pH, temp, ammonia, nitrite, nitrate....

Anything else changed at all... i.e feed rate, plumbing, cleaned tank?????

I'd get that foam raft out fast unless you are sure it was a new piece.
It could be contaminated from what it was packaging.
Don't know if Koi would try and nibble it - that may not do them any good

Ok, sorry for the late reply, had some big storms around here, knocked out the internet for awhile.

Anyways I just re-tested the water and here is the results:

PH: 7.4
Ammonia: 0
Nitrite: .25
Nitrate: 40

This system is almost always identical to that when I test, it hardly ever varies.

RupertofOZ: No, nothing else has changed, I actually have been so busy working on other stuff I haven't had time to do the upgrade stuff I wanted to with this system, so besides feeding and harvesting I really haven't done anything.

Also another update, no more deaths, but the goldfish don't seem to be acting like themselves now. I am going to pull out the styrofoam raft right now just in case that helps.

Also the raft I have in there is new styrofoam, nothing thats been used before.

Any other ideas? I have a feeling this tank is going to be fishless in a couple days if I don't figure out what is going on.

Decided to take a couple pictures to help, these pictures are of the next fish that is going to go. It is acting really sluggish, doesn't try to swim away from the net when I am trying to get it.

Out of the water it doesn't flop at all, once put back in it was upside down for about 30 seconds before it righted itsself and started swimming around.

The pictures are not that great, sorry.

Hmmm... tough one, I can't put a handle on it

Well I just added salt, should be enough to up it to 1ppt, since that seems to be the general cure-all for fish problems. I have never had a problem with this system so I never salted it.

Also anyone have opinions as to whether the styrofoam could have caused the issue? I am thinking of looking in the stomach of the next fish that goes to see if I can see anything out of the ordinary.

I was just talking with my wife and she said that we hadn't put in the mint plant on the styrofoam raft yet when the first fish had died. So I am going to guess the mint plant or the styrofoam don't have anything to do with the fish dying.

I have however removed that from the tank just in case, still looking for any suggestions.

Grasping at straws a bit... but just what sort of "styrofoam" are you using... what was it originally intended for??

Reason I mention it is because some styrofoam panels used as building insulation... are soaked in fire retardant....

Sounds like it could be slow poisoning to me too.
Its a devil and deep blue sea scenario.. if fire retardant or similar chemicals are in the water salt won`t help much. Massive water changes would dilute the poison but also stress the weakened fish in the process.
A hospital/quarantine tank maybe the best bet.. it would guarantee non toxic water and salt to help reduce the stress.

Make sure the system doesn't have any brass, copper, zinc, galvanized metal or any other non stainless steel in contact with the system water. These metals may not be immediately toxic to fish in small quantities but over time in a recirculating system, they can build up in the fish causing deaths.

The idea about using a hospital tank is a good one and hopefully you can track down what is killing your fish.

mweidner, just by chance, are either of the two of you using any thing different on your hands, like hand creams or oils?

So a few updates. The salt seems to be helping, a few hours after I put the salt in the fish that was in the worst shape started being able to swim more normally, and now over 24 hours later still seems fine. I am not sure we are safe yet, but I am feeling a bit better.

To answer some questions, there is no metal in the system, the tanks are plastic bins, the hoses are garden hoses, everything I used to build it out should be food safe. My wife uses lotion on her hands, but she doesn't do much with the fish, she feeds them once per day so I guess that could be an issue.

The styrofoam was used as packing for a light I purchased so I am quite sure that it wouldn't have flame retardant on it.

So in summery, the problem might be correcting itself, which kind of worries me, if I don't know what the issue was, I didn't fix it and chances are it will return sometime.

Don't suppose you did a nitrite test did you???