Pond Boss Forums INTRO Questions & Observations Fish kill in aerated 2 acre pond

Our 2 acre neighborhood pond just experienced a 40+ LMB fish kill. It's been over 100 degrees for the last 10 days or so. The pond is about 10 deep in its deepest part. There are 3 aerators operating 24x7. My speculation is it's due to overcrowding since no one harvests any fish. Any thoughts? I still see all the little fish at the surface of the pond

When it's extremely hot, it's my understanding that aerators should only be run from about 8PM to 8AM. It avoids mixing very hot surface water into the column.

+1 on what John said. I have read the same thing. When it runs during the day you push your cool water up and it heats up and as the cycle goes on cool up and hot down you eventually have super hot water. I have also read that night is when you need it most because what plant life you have will not be releasing o2 during the night like they do during the day. I bet if you do as John says and shut them off during the day and run them at night you won't have any more problems.

Here is a perfect scenario where a surface air type fountain would be a good thing taking water off the top 1 or 2 feet and blowing it into the air to help cool it down and oxygenate it as well. What you do want to do is mix the hot water during the day diffuser air by night and fountain air by day is the best case scenario if you can do it.

RC

P.S. In this kind of heat we are all at risk of the fish kill though that's for sure.

Many things can cause a fish kill. Hot water holds less O2 than cool water but don't confuse cool water with below thermocline water with no/low DO. Rapid temp changes can also kill fish even with no DO problem. So can bacteria or disease issues. Fish under stress are more susceptible to problems so it could be a combination of factors.

Do you know the DO ppm in the pond?

Ummm, maybe not. Here's a real life experience.

1 ac pond. 18' deep at max depth. Thermocline set up around 10 feet, and the water at 17' was 60°F. As pond warmed up in the Spring, surface temps got to 78°F and the trout showed signs of stress and I saw one mort. So, I purchased a low temp t-stat to run the aeration system only at night, when ambient temps were below 70°F.

Only running it at night, one single 9" membrane diffuser in 18' water depth when ambient temps were below 70°F mixed the whole water column, and the water from top of pond to bottom was 75°F. Trout died.....

I don't have O2 readings from that single event to post. I WILL be starting up an aeration system in a very deep pond this weekend and will take O2/temp readings. The aerator in the deepest part of the pond will be set 10'-12' up off the bottom of the pond to see if a cold water refuge for trout can be had while keeping high enough DO levels for their survival.

Personally? I'd prefer 95°F water temps with O2 readings at saturation levels or at super saturation levels than 85°F water at 4 or 5 mg/l levels.

Our aerator runs 24/7, never had an issue. But do not have trout.

I am asking for some guidance. I recently had a pond dug for me in Southwest Wisconsin. The pond will be slightly less than 1 and 1/2 acres and will be approx. 20 feet deep at the dam and I am looking at a windmill aerator, specifically an AMERICAN EAGLE WINDMILL system. My questions are thus...has anyone had experience with this system? good? bad? recommend another company's system? The pond is 3/4 mile from electricity so I am somewhat limited in my choice for aeration.
lastly where you position the diffuser system in the pond

Any thoughts concerning effects of over population? Very little harvest ever in this pond

Overpopulation is always a concern. Fish that are poorly conditioned due to not enough food are stressed. Stressed fish are always more susceptible to problems. Poorly conditioned stressed fish in conjunction with high temps and low O2 (but not at lethal levels) are more apt to die.

I would think but have nothing to prove this but if the kill the original poster exexplained said only lmb were killed he ciuld still see the smaller other fish still alive..does that mean the lmb are more prone to die off on whatever caused it...i just find it hard to believe that temp or air just caused one species to die off ...just my thoughts

I think their was a complicating issue. I sometimes aerate a lot of ponds 24/7 that are just over 5 feet deep without problems.

Is it possible the aeration was not sufficient?

I would look at the stones in the pond and see if you have bubbles on the stones. I have had fish kills in tanks that have been from to much air.

I have changed our air from 24/7 to only run 12 hours because of too much air. Running it at night has kept the water cooler longer for our fish.

Cheers Don.

Donno:

Can you define the "too much air" statement? How do you know it was too much air?