Can someone please post details? I'm seeing a lot of posts about just aerating at night to keep pond temps down, but I'm not seeing ANY posts with hard data supporting their theory.

I'd love to see pond temp and O2 data aerating 24/7 vs. only at night.

In my experience with trout in the pond, aerating only at night when the night time temps were below 70°F did absolutely NOTHING to keep the trout alive any longer in the pond.

With that being said, I have a customer that has trout in his pond, and runs a volcano type surface agitator and a bottom diffusion aeration system with the diffusers set no deeper than 40% of max depth of his pond and he has been able to keep trout alive for 22 months so far, running them 24/7 during the spring/summer/early fall.

So if anybody has data please share it.

The main reason I aerate at night is to keep my compressor's temperature down. (Will you believe that?)

I always figured that water temps would be lower as a result, and since I'm a typically rationalizing (as opposed to rational) human being my figuring has always been good enough for me.

I kind of think year-round trout this far South is a poor crap shoot, unless you have a good, steady cold spring flowing.

The 64 thousand dollar question.

Had a partial fish kill last year (only the biggest fish) when I was trying to aerate mostly in the day time with the incorrect theory of turning the water over when it was super saturated with oxygen during the daylight hours. I was on vacation at the time with only an email of what was going on. Had grandson pick up the dead fish and turn on the aeration 24/7 with no further problems.

I have the timer set to shut down air during the hottest mid day time period but have no idea if it helps or not with the water temps. Had the scuba gear on to clean the diffusers a few weeks back and the temperature to feel was not much different from top to bottom. That said, when on the surface swimming and you approach the diffusers, the water will feel noticeably cooler as you get near the diffuser plume. So I know there is at least a slight difference in temp top to bottom.

No help here esshup. Just a few of my observations.

I was thinking about this and I am not really sure how you could do an accurate comparison. Year to year comparisons won't work because so many different weather factors could be different. One month 24/7 and one month a night won't work because of weather again. How would you 100% accurately compare?

At our place I have some night time running this year and there is a difference in water temp this year versus previous years. Is it due to the aeration schedule? I THINK so, but no scientific proof.

Esshup, what kind of temperatures and O2 readings are you getting there?

I have a bunch of data on my pond, but it was not collected with just Temp, DO, and air time as the focus. So, it does not really lend itself to good test results (too many changing variables - nature and personally induced) I have monitored water temps and found that running the air during the hot summer days seems to increase the temps while reducing the DO levels. I can't say for sure which is better...high temps/higher DO vs lower temps/lower DO. Decreasing air time certainly decreases DO levels. A very simple test would have to be done with two BOW's side by side, one with circulation and the other stagnant. I wish I had twin ponds, but even neighboring ponds can be different.

I think this type of data collection would be difficult to evaluate given such an ever changing environment (what wbuffetjr was saying).

My theory is that, given the volume of water in a BOW and constantly and thoroughly exposing it to warmer ambient air (as with an aerator)...it will heat up. Smaller BOW's are much more susceptible to a faster temp change.

When no aeration (water turning over actually) is applied, the deeper water stays deep and cools or stays cool being stagnant against the underlying cooler soils. The surface water heats up quite a bit during the day, but remains there on top and cools back off quickly at night time with the cooler temps because it is close to the surface.

The real defining point whether a pond heats up (or cools of in the winter) with aeration lies in the Delta T's (the differnces between the water temps and the surrounding air or soils that can affect the water). Most of our sub-soils are about the same temp regardless of the region (within reason)...most of our ponds (small BOW's) will have similar deep water temps without aeration. This yields a small detla T in general (pomd water temp versus surrounding soil temp). But, depending on climate...the delta T between water temps and ambient air can vary greatly. simply put, common knowledge that warmer areas have more trouble with hot water. Shaded versus non-shaded waters will make a big difference to. Air to water temperature exchanges are known as convection heat transfer while the effects from the sun are radiant in nature. I would think the soil to water transfer would be conduction.

I believe that the delta T between the ambient air during the hot summer months has more of an affect on changing the water's temperature than does the conduction transfer from the surrounding soils. Partly because the air to water interface is immediate (no insulation) whereas the conduction between the soils and water is spread out over several inches of soil that has to all change in temp together to make a noticeable change (the temp gradient is gradual through those inches of soil - it acts like insulation). The Delta T between water temp and soil temp is likely to be higher than that of the ambient air and water surfce, but the heat transfer through the layers of soil could be lower. Throw in the radiant power of the sun along with the convection transfer and the water will heat up...given the proper detla T.

Other contributing factors would be wind action and humidity (I think you mentioned the effects of evaporative cooling in a different thread -somebody did anyhow). The lower the humidity and the more wind action...the more cooling from evaporation. I really can't say how much this effects the pond temps, but it's still a factor.

Just my theory, I'm not trying to convince anyone, but it seems to back up my loose pond readings. Any heat transfer wizards among us that could put some calcs on paper?

I think you are right when it comes to running a volcano where it will lower surface temps instead of running only diffusers and seeing little if any reduction in water temps during the summer. Some experimenting is going on right now and seeing how adding a sprinkler can reduce surface temps 7 degrees. It's too early to say any more at this time, but maybe more info later on.

Like the proverbial cobblers kids shoes, my personal pond has been neglected this year. I was not able to source enough tilapia locally so I didn't stock tilapia in my pond this year - my customers come first. SO, there is a filamentous algae bloom along with a pretty heavy planktonic bloom. We have been really dry, the pond is down about 4' vertically from full pool in May. I've never seen it this low so early in the year.

I was at a pond 180 miles S of here last Friday (60 miles due South of Indianapolis) that had no aeration system. 10 ac pond. Total pond depth was 28 feet. Visibility on the Secchi disk was 6 feet. Lots of Naiad in the shallows - down to 3'-4' water depth. Surface water temp was 79°F, running 100% O2 saturation level at 1' water depth, O2 levels dropped to 3 ppm at 8' water depth and water temp dropped to 72°F. 10' depth water temp was 70°F and O2 levels were in the 1.3 ppm range and quickly dropped to 0.8 to 0.5 the deeper I took the readings.

Theo, the goal for that particular pond with the trout in it was to keep trout alive all summer long. It took 3 years of trying different aeration scenarios, but it looks like we have found a combination that works. As you know, this summer has been MUCH warmer than last summer, so in September when the water temps start to drop and the trout get more active we will see if they survived this summer too.

My consultation rate is $200 an hour. $50 of that goes to the junior engineer who would actually do the work (he took Heat Transfer more recently than 40 years ago).

esshup, I am honestly surprised that someplace as close as Northern Indy has been extra hot and dry this year. We had a cool, wet late Spring and good rains for the last month or so (although with some hot streaks); my ponds are down about 7"-9", typical for this time of year.

I discussed this briefly in another thread, but I'm particularly interested in the location of the compressor, and how it affects temperature. Here's my theory: A pump or air compressor pulls in air around it, and directs it to your diffuser. If the surrounding air is 95°F, theoretically, your pump is directing 95° air into your pond. Those little 95-degree air bubbles will heat up the surrounding water as they travel to the surface. Also, the pump itself is creating heat, which could potentially cause 100°+ air to be sent to your pond. If your pump is in direct sunlight, that could exacerbate the problem even more, versus keeping it in a shady location. Is there any merit to this "theory" of mine, or does the temperature of the air bubbles not matter as much as I think they might?

I think the running temp of the compressors is more in the 120°¯F+ range. With that said, how much does the water cool when it evaporates in the hotter air?

Theo, I'm about 30 miles SSW of South Bend. The rains have formed just to our East, or split and gone N and S of us. That big storm event of last Monday? We had 1/2". We haven't had a drop of rain since Aug 10th. Our spring was wet and late, but the faucet shut off the end of May.

My pond is a groundwater pond, and it is affected by evaporation rates, transpiration rates and how much the farmer 1/2 mile away runs his center pivot. When he runs his center pivot, I can drop as much as 1" vertically per day.....

That's the reason why I refurbished the pond and dug it to 22' deep 11 years ago.

Operational temperature of a Gast rotary vane is 205F; thermal shutdown at 256F.

Thanks Bill! Do you have operational temps of other types of compressors, such as rocking piston and diaphragm?

Contact Gast Mfg engineers for operating temps of the other compressors. This is where i got my info. I suspect all run close to 200F.

Thanks Bill, I'll do that and also contact Vertex for information on their compressor operating temp.