Fish die off

[theboyzmom]

Hello - new to the forum - I have an about 3000 gal pond that varies from 5 feet deep to a couple of feet. I have 6 (was 8) koi in there that have lived happily until a couple of days ago. I also got some junk fish in there somehow. Anyway, the water started clearing after a murky start - now I have fish dying - first it was the trash fish - about 10 of them - now I have lost two Koi. Both smaller under 6 inches. I have vacuumed it out (about a week or so before this began). I run a media filter, fountain and a aerator in the winter and when it is hot out. Any ideas - the fish look fine - no red gills or red on the body. I am so sad I lost two and would like to keep the remainder happy - most are bigger than the two deaths.

 

[JRS]

Welcome to the forum. Some more info might help. How long has the pond been set up? Have you done any water tests-ammonia and nitrite especially. Junk fish-minnows? How big are the surviving koi?

 

[theboyzmom]

Thanks for the welcome! I have not water tested yet - the pond has been up for four years without issue. the Junk fish are varying sizes - some kind of carp - we think the birds eat the eggs and drop them. the surviving koi are about 8 to 12 inches ( a couple smaller but most are in that range)

 

[Lisak1]

Have these fish been in this pond for four years? I ask because it would be odd for koi to be 8-12 inches long after that many years.

Any chance you’ve had run off or overspray of some kind of yard chemical into the pond?

 

[Mmathis]

Hello and welcome?

Is this pond lined or is it a natural pond? It sounds concerning that the depth varies by so much.

Please include some pics.

 

[poconojoe]

It sounds like whatever happened, it was sudden and because there has not been any physical damage to the fish, I would guess it could be a water quality issue.

It could be some chemical or other pollutant somehow washed into the pond. Has anyone sprayed fertilizer anywhere near the pond?

It could also be your fish waste that's gotten out of hand. This could happen if your filtration is inadequate or the pond's ecosystem is out of balance.
This is why without a good liquid reagent pond test kit, we can only guess. Get a test kit and post the results.

Do you have any plants? Plants are an important part of the ecosystem. They help filter out excess nutrients produced by fish waste. Lots of plants are needed. That, along with biofilm growing on everything and beneficial bacteria in your filter help keep things under control.

Describe your filter. Maybe it's inadequate.

You mention you run a media filter, fountain and aerator in the winter and hot days. This could be your problem. They should all be running 24/7/365 to oxygenate the pond and keep the beneficial bacteria healthy.

Could be a lack of oxygen that's killing the fish. Its imperative, especially when the weather is hot, to keep the pond oxygenated. Surface agitation is the best way to do that.

You mentioned vacuuming the pond. That's ok for removing the heavy sentiment on the bottom, but you want to keep all the growth on the rest of the liner in tact. That biofilm is part of your filtration.

 

[j.w]

@theboyzmom

 

[theboyzmom]

Some of the fish have been there the entire time - I have added a few - normally I buy them relativily big. LOL Anyway, this is a dug pond. I have had the aerator on now for four days - I had one dead small koi last night but they seem active and happy today. I have made sure not to get the carpet algae off the bottom - I know it is important. I just got the muck out. I also have lily pads - but they are not doing very well this year either. I will run out today and see if I can find a pond test kit.

 

[Mmathis]

@theboyzmom I think what I meant is, does the pond have a liner (rubber or PVC), or is it a dirt/mud/clay bottom.

 

[Lisak1]

"Relatively big" must be relative. Any koi under 12 inches is still on the small side.

Anyway - were these new fish added recently?

 

[theboyzmom]

@theboyzmom I think what I meant is, does the pond have a liner (rubber or PVC), or is it a dirt/mud/clay bottom.

Sorry - it has a liner - not sure what kind - the guy that built it died but he called it pond liner.

 

[theboyzmom]

"Relatively big" must be relative. Any koi under 12 inches is still on the small side.

Anyway - were these new fish added recently?

No new fish this year. The fish look really big to me but I only see the smaller ones generally at the pond places. why is is strange that they are that size after that time? Should they be bigger?

 

[theboyzmom]

Ok I went and got a basic test kit (well - the only one I could find on a Sunday!) PH 7.5, nitrates and nitrite were negative. KH was 80, GH was 60. It did not test for Ammonia but the fish look much better and no new deaths. They are now active and eating. Perhaps the Aeration was the problem.

 

[Lisak1]

Should they be bigger?

Generally speaking, yes. A koi that is four years old and under a foot long would be outside the norm. A whole pond full of them would be really unusual. I would LOVE koi that stayed that small.

I’m glad things have settled down for you but I highly doubt aeration was the issue, especially since you mentioned the smaller fish were dying. Oxygen depletion will hit the bigger fish first. A 3000 gallon pond with a low fish load - doesn’t sound like an O2 problem to be honest.

 

[SarahT]

Welcome to the Forum. Sorry for your fish loss. I think pictures could help, of the pond and a couple of fish. Look for a water testing kit that tests for ammonia, as that is a critical factor in fish and pond health.