Pond Boss Forums Thread Like Summary - Aeration at night during hot weather?

I moved the aeration at night replies to the "Algae and Dying Bluegill......a connection?" thread here for future clarity and search parameters.

Snipe, I agree to a point. Years ago it was said to only aerate at night when you have trout in the pond because they will live longer. Only aerate at night when the air temps are below 70°F. The cooler night time temps will put more O2 into the water for the trout. Nobody could furnish temp or O2 data though, they were just saying what someone else said without data. It took 3 years of testing in my pond to prove to me that it was a fallacy. I bought a temp controlled on/off switch, and had the aeration system only turn on when temps were below 70°F. The trout died quicker than if there was no aeration at all which allowed the thermocline set up and keep water cold down at the bottom of the pond. Turning on the system at night mixed the warm upper water with the cooler bottom water and the volume of O2 in the pond wasn't enough to oxygenate the cooler water to a high enough level and the trout croaked.

Without any aeration at all, there was not enough O2 to keep the trout alive below the thermocline, but there was enough O2 in the water right at that thermocline level to keep the trout alive until July 4th.

In another pond a few years ago that was much deeper we were able to keep trout alive all summer long by setting the diffuser 12' off the bottom and letting it run 24/7 along with a surface agitator in the 1/2 acre pond. The O2 levels were high enough in the upper water level to allow enough O2 transfer to the upper thermocline layer to keep the trout alive.

I really think that the people with the hot water in the summer would be much better off going to a surface agitator type aerator than a bottom diffusion aeration system to put O2 in the water. How many fish farms do you see running surface agitator systems vs. bottom aeration systems?

Another thing to consider is that if the bottom aeration system is sized to run 24/7, and someone only runs it for a few hours per day, they run the risk of under-aerating their pond which causes issues of it's own that won't help their situation.

Think I'll join in this conversation.
Here's what I've found: Different species have different temperature tolerances. Different sizes of those different species have different temperature tolerance. Those species have different lower lethal dissolved oxygen requirements. For example, Big gizzard shad can't live in water much below 4 ppm DO, but can tolerate temperature into the 90's. Largemouth bass, especially bigger ones, can't tolerate temperature consistently 87 or higher...they have to have a refuge. One study on a lake I've helped manage proved bass in that lake would stick their noses into the thermocline, where DO was about 3 ppm and temperature was in the high 70's, during the hottest months of the year, when surface temp was 90+, and 83 just above the thermocline.

Here's my response, based on decades of doing what I do and studying fish behavior. Largemouth bass are distressed when water temperature exceeds 83. If consistently above 87 for an extended period (a week), the bigger, older fish begin to die.

I've had several lakes under management in Texas where we saw that phenomenon firsthand. Had one client, in particular, who bought an aeration system from a vendor, had it installed, liked it so much he decided to add another one just like it. (The first one was sized exactly for this 10-acre lake.) So, he had twice as much as the lake needed. I bet the lake was turning over 3-4 times daily, at least. One hot July morning, he rang my number. "Seeing two or three big bass floating today. Why?" There wasn't enough logic to give him an answer. Then, it happened again, then again over the next few days. The lake was three years old, loaded with fat, young, healthy feed-trained bass that were two years old when he stocked them at a pound and a half, average. Water was fresh and healthy, visibility was 30+ inches, no toxic bloom. Fish fed well, behavior seemed normal, except feeding activity had dramaticall slowed. I had him get a thermometer and begin checking temperatures all over the lake in 2-foot increments. The entire lake, top to bottom, was 87 degrees. I had him turn off one of the systems. After three days, no change...and a few fish were floating each day. So, I had him put the remaining aeration system on a timer from 10 pm until 9:00 a.m. Within four days, the temperature dropped to 83 degrees and fish stopped dying.

I've seen this phenomenon happen over and over with Largemouth bass. It happens with bluegills to a lesser extent.

O.K., a question for the guys that say to only aerate at night to keep the water temps low.

At what water temp would you want to do this, and at what water temp is this not required? i.e. if pond water temps are 80°F, is it necessary to do this or is this only required when surface temps are pushing 90°F? 85°F? 75°F?

I have yet to see anyone on here post their water temps in ponds that they only aerate at night vs. 24/7. And those numbers would have to be correlated with ambient temps and amount of sunlight. 90°F ambient temp with full sun is hotter to the pond than 90°F and heavy cloud cover is it not?

To me, without numbers to put to the puzzle, then we are only guessing about the water temps and O2 levels. We shouldn't be guessing................

I agree that this would be excellent experimental data to obtain. However, that is a very difficult experiment to run in the real world.

Even two similar ponds on the same property would probably have different circulation patterns so the temperature profile for the pond with bottom aeration might be affected by other factors relative to the pond with aeration 6' off bottom.

Also, I would think that "time of year" should be a significant factor. The peak average air temperature for most of the U.S. comes at roughly the last week of July to the first week of August. If your pond is already within a few degrees of the "danger zone" for your fish by the middle of June, then I would switch to aerating only at night because that pond has six more weeks of projected warming.

I guess the best experiment would be if someone had two side-by-side "roller pan" forage ponds. Maybe they could run the experiment for the forum.

I do like your question and thinking. Maybe the forum experts should give the advice that if you do experience a summer heat fish kill, then you should immediately run out and measure the temperature profile of the water column in your pond. That would then give people an idea when they are approaching the danger zone in the future for their particular pond and fish population.

Likewise, if you see a large rain event in the forecast, go to the pond and get a temperature profile. Then if you suffer a cold rain induced pond-turnover fish kill, you might know the temperature profile for when your pond is most susceptible to that problem.

esshup, that's a good point. Also a point I personally take into account.
If we have to aerate, it's best at night-in the hot time of year- for the simple fact lower water temp holds more O2 than higher temp water.
75-80-85-90 has nothing to do with it if you don't know what your BOD is.. but if your water temp is over 85 and your night temps are only 80, you still better be aerating at night if nothing but for the simple fact BOD is highest at night.

Scott, this is not a guess to me.. because there is only a minimum we are trying to stay above. When I hit 80-81 I'm turning it at night.
Now, as days get shorter-even though highs for the day may still be 104, it's for a much shorter period and the nights at 55-60 are much longer and I'm sure your pond temps are dropping just like mine. I'm 71 degs on the surface today but when I dropped below 75 I quit aerating at night and moved to 2am to noon. In 2 weeks I'll be 8 am to 7pm to keep temps up-not O2-to extend every minute of growing I can.
If we say at 80 you need to start aerating at night we might get jumped on when someone has a fish kill because they had a monster load of fish, a massive bloom, feed 4lbs per acre a day and a cold rain come in and a couple of cloudy days but water temp was only 78 so there was no aeration at the time it was needed most but Billybob's pond had no fish kill because he had clear water and low biomass.
How do we set the standard to gauge this? We have many moving targets with countless variables.
Nothing but respect for ya Scott, you know that. This is in the spirit of conversation.
EDIT: I quoted a comment and it didn't allow attachment...weird..