I had six trout go belly up in one week a few weeks ago. Checked water temp profile and water temps were fine. D.O.was a little low in the deeper water,but not enough to cause apoxia at about 5 mg/l. However long story short,which includes a replaced probe, and even regular calibrations, I don't trust my D.O. meter. I felt it was reading too high this winter under the ice and may have been reading to high in the trout pond.

So knowing that 99 percent of the time fish morts and fish kills are due to low oxygen, and I presently have about 400 + pounds of brook trout in the pond, I started running the diffuser 24/7 vs. only running it at night as the idea was it could raise water temps too high during the warmer part of the day if you ran the diffuser 24/7.

Been running the diffuser only at night for at least 10 years and guess what I learned? By running the diffuser 24/7 overall water temp in the water column only went up 2 degrees F. on days where highs were in the 90 degree range. That is, the water was 62 F. from top to bottom vs. about 64 on top to 62 on the bottom when running the diffuser only at night.

Therefore in my steep sided 1/10 acre pond that is 88 by 59 feet and has a maximum depth of 9 feet, and an inflow of aerated 51.6 F. well flow of 45 gpm, it's better to run the bottom diffuser 24/7.

I think I got away with running the diffuser only at night in the past because the pond was younger with less oxygen robbing sediment.

I also have extensive Chara in the pond, that although it produces D.O. during the day, may reduce oxygen levels when it respires at night.

Just thought I would pass this along for those of you with trout ponds or are considering one. The idea that one must only run the diffuser at night may be overrated.

Btw air flow is about 2 cfm.

Cecil, I found that when the surface water temp is high (in the mid to upper 70's) even just running the diffuser at night when night time temps were below 70°F mixed the water enough to raise the lower water temp above 70°F. So, my finding corresponds to yours, that running the bottom diffuser at night or all day long didn't make a difference in the resulting water temp change. Running at night or 24/7 was the same result.

What was your surface temp before running the diffuser? 64°F?

Surface temp before running the diffuser 24/7? 64 F.