Pond Boss Forums AERATION Should I aerate? Aeration, muck, and thermal refuge

GPH is gallons per hour. mg/L is milligrams per liter.

In my real world example in my previous post above, that is how many gallons of water per hour is brought up to the surface to interact with the O2 that is in the atmosphere. Water doesn't have the same O2 levels in it when it's not moving due to aeration - the lower in the water column the O2 reading is taken, the lower the O2 concentration is. The only time that I have not seen that happen is in crystal clear water that had FA growing down on the bottom of the pond in 14' of water. That was temporary, as the water warmed up a few weeks later, a phytoplankton bloom started, and visibility diminished, killing the algae in the deeper water and the O2 levels there plummeted.

Water that has a bottom diffusion aeration system in it gets the majority of O2 transfer to it from it interacting with the atmospheric air, NOT the air that is pumped into the diffuser(s) in the pond.

Using an optical O2 meter I have never seen calm water in a pond that was not aerated or mechanically agitated at 100% O2 saturation levels, no mater what the water temperature. I HAVE seen water at saturation levels at the surface when the pond had both bottom diffusion aeration and surface agitation systems running at the same time.

When you say "an acre of algae is producing way more O2 than the surface water can hold", please define the thickness of the algae (wet weight density of algae in kg/gallon) and the thickness of the surface water that you are referring to. Are you referring to an O2 production system or algae in a pond? I am asking these questions because I cannot agree or disagree with statements that are not quantified.

In a production O2 generating system where algae is used to produce O2, 5 kg to 10 kg of wet algae will produce between 55g to 83g of O2 per hour in optimum conditions. In a pond, when sunlight no longer reaches the algae in the pond, it stops producing O2 and starts consuming O2, at the detriment to the fish that are in the pond. 5 kg to 10 kg of wet algae will need to consume between 10g to 600g of O2 per hour that it is without sunlight.

I don't do well with theoretical calculations, but I can do them when required. I prefer to go out on the water and measure. There are way too many variables in real life. That's why I have a YSI Pro ODO meter.

In ponds, theory diverges from what actually is happening in the pond very quickly. Surface water mixes with non-surface water pretty quickly. Dump a quart or two of dye in a pond and see how fast the whole pond changes color when the pond does not have an aeration system or fountain in it. If there is a thermocline in the pond, the dye will not mix into the lower water depths as fast as it mixes with the upper water column. (below the thermocline vs above the thermocline)

So, circling back to your statement that "I figure most of the dissolved oxygen added to the pond by aeration comes from spreading the O2 that's naturally produced in shallow water during the day to deeper water that's able to absorb it, instead of it rising up and outgassing into the atmosphere where 99% of the O2 produced by the pond during the day ends up. The amount that's directly added by bubblers is minute.", I have to strongly disagree.

That is why in real life that pond owners that have no bottom diffusion or surface agitation aeration systems in their ponds AND have a secchi disk reading of <12" due to an algal bloom have a very good chance of having a summer kill at night during the summer due to O2 levels in the pond dropping below the levels that are required by fish to survive.

In a HOA customers 18 acre non-aerated pond, they were experiencing both summer and winter fish kills. Secchi disk readings were anywhere from 8" to 16" during the summer, due to phytoplankton blooms. Their budget could not support installing a bottom diffusion aeration system in the whole pond that 1st year, so we only installed a system in the North half of the pond that ran 24/7. That August, the half of the pond that did NOT have an aeration system in it experienced a summer kill while the other half of the pond did not. Wind was from the South, and 2-3 days later the dead fish floated to the North side of the pond. If I wasn't there the day after the fish kill event to observe where the dead fish were before the wind moved them around, I wouldn't have known that and would have assumed that the fish died all over the pond instead of the half of the pond without aeration.