Pond Boss
Posted By: Mary Davis Should I run the aerator just at night? - 07/30/21 07:06 PM
I live in Washington state where the weather rarely gets above 90°. I have about a half acre pond which at the deepest is probably 12 feet. I run an aerator 24 seven at about 8 feet deep. In July we had some rare temperatures over 100 for two days. We lost about 20 of our trout. My neighbor suggested just running the aerator at night when it gets that hot. He said I was sending hot air down to the bottom of the pond which is not a good thing. It seems like everything I read suggests running the aerator 24 seven. We hopefully will not have temperatures that high again, but if I do should I turn the aerator off during those high temperatures at least in the daytime? I am certainly no pond expert and can get overwhelmed when reading some of these posts. So if you can keep the answer fairly simple I would appreciate it. This is the first time we’ve ever lost fish so I know it was connected to the heat wave, just not sure if the aerator contributed to the problem or not.
Posted By: Steve_ Re: Should I run the aerator just at night? - 07/30/21 10:37 PM
Hi Mary, your neighbor is correct, you don't want to run your aerator when the air temps get that high. What happens is your aerator is pushing lots of water to the surface where it heats up quickly, and doesn't allow the deeper water to provide a thermal refuge for your cold water fish. If you've ever gotten into an outdoor swimming pool for the first time of the day, you'll probably notice that the top of the water is a lot hotter than the bottom, but after people have swam in it for a while and mixed it up, all of the water will be roughly the same. Kind of the same thing that can happen in a pond.
Posted By: esshup Re: Should I run the aerator just at night? - 07/31/21 06:11 AM
Originally Posted by Steve_
Hi Mary, your neighbor is correct, you don't want to run your aerator when the air temps get that high. What happens is your aerator is pushing lots of water to the surface where it heats up quickly, and doesn't allow the deeper water to provide a thermal refuge for your cold water fish. If you've ever gotten into an outdoor swimming pool for the first time of the day, you'll probably notice that the top of the water is a lot hotter than the bottom, but after people have swam in it for a while and mixed it up, all of the water will be roughly the same. Kind of the same thing that can happen in a pond.


Umm, not exactly. It all depends on what temps the upper water is. I did just that, using a thermostat that would only allow the aerator to be on when the ambient temp was below 70°F. Didn't contribute to the trout living any longer, in fact I think they died quicker than if I would have left it off and didn't disrupt the thermocline.

There will be an aeration system available to pond owners later this year or early next year where you can oxygenate the cold water where the thermocline starts and not disrupt the warm upper water. I can see it in some ponds that are deep allowing the pond owner to have two complete different fisheries in the same pond, a cool/cold water fishery and a warm water fishery.
Posted By: DonoBBD Re: Should I run the aerator just at night? - 07/31/21 02:46 PM
This is what we do for our Yellow perch pond. In the winter months we run it 24/7 but in the summer it is 7pm to 7am and only in the shallows.

When I would aerate the deep water air-stations we would loss fish. Even when we would turn on the deep water air-stations when the surface temp was 55F we would loose fish.

We now just run air-stations in the 5 foot depth for 12 hours at night. Along with our waterfall that runs 8000 gallons per hour into one deep end of 12 foot.

We haven't lost any perch since we have change this and this year we have the best young hatch we have every had. We did have some rainbow trout but a pine Martin decided to clean them all up for us.

Cheers Don.
Posted By: RaulPNW Re: Should I run the aerator just at night? - 07/31/21 07:31 PM
We lost over fifty rainbow trout during the recent heat dome, and since then I’ve only been running the bubbler aerator at night. I’ve been thinking about running cold tap water into the pond during the next heat wave or burying pipe at least four feet deep and making a reverse geothermal loop to pump warm pond water out, circulate it and then send the cooler water back into the pond. Has anyone tried either of these, or anyone have any other ideas?

1/3 acre pond, 12 feet deep at center, about 2 hours west of Seattle, rainbow trout
Mary,

The starting bit of information you need to keep your trout happy, is cold water holds a larger amount of dissolved oxygen than warm water. (All other factors being equal, of course.)

You run your aerator to add dissolved oxygen to the water column in order for your trout to survive. No one can give you the exact right answer for your situation, because aerating during hot temperatures is almost always a delicate balancing act.

With no aeration during the summer, your pond should stratify. (To oversimplify, there will be warmer water at the surface and to a certain depth, and then a pool of cold water at the bottom [or at least an area where temperature decreases sharply with depth].) When you aerate, you add dissolved oxygen to the water column (good), but the trout lose their refuge of cool water (bad). You are going to have to experiment to determine the correct balance for YOUR pond of adding oxygen through aeration versus losing your cooler waters. To experiment, you must have good data. Hopefully, you have a good thermometer. Start collecting some records for your pond. If you have a lot of time/money in your trout, you might also consider a dissolved oxygen meter.

You already have had several of the aeration experts from the forum makes comments in your thread. I hope my little note will make it easier to understand their advice and to keep your trout alive and happy!

The good news is - that was a record-breaking temperature event in your area. Hopefully, you don't have to deal with another event that severe for quite some time.

Good luck on your project!
Raul,

Sorry about your 50 rainbows!

Yes, there have been discussions about using supplemental cold water and even some discussions of geothermal heating/cooling loops. (Hit the search icon, and then play around using the Advanced Forum Search function.)

Is your cold tap water chlorinated? How much dissolved oxygen is in your tap water? If you need to flush chlorination and add oxygen, there are some discussions of how people treat low-oxygen well water before supplementing their pond water.

I suspect in your case (and Mary's case) that if it was possible to get a supply of cool, oxygenated water to the deep section of your pond for even ONE WEEK, then a lot of trout would have survived that brutal heat wave.
Posted By: RaulPNW Re: Should I run the aerator just at night? - 08/02/21 02:19 PM
Thanks FishinRod, I'll poke around and see if I can find those threads. The water is chlorinated so I'd have to remove that, and I thought spraying the water should add some oxygen. If I decide to put the geothermal loop in I'll post the results here.
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