Those are pretty good readings, makes sense that the DO is low below 8 feet, what time of day did you take the readings? Try taking some at night as well.
I wouldn't put the diffuser on the bottom - with DO that low you could force a fish kill, check youtube for that exact same scenario..
I think you might have similar results with no aeration but that is just me, my lake is the same size and depth and I have no aeration, similar DO results. Honestly dont over think it, your fish are super healthy from what you have said so other than water clarity and algae which you have started to clear up why bother throwing a wrench into the mix.
Check out my recent post on riparian/hyporheic zones, that might make a difference for you was well.
Cheers.
Let me clear up some misunderstanding.
1) The goal of a bottom diffusion aeration system is to bring O2 to the bottom of the pond, so the fish have the whole water column to utilize, AND bringing O2 to the bottom of the pond will allow aerobic bacteria to colonize the organic matter at the bottom, which in turn will greatly reduce the amount of annual muck accumulation.
2) Placing the diffusers on the bottom in the deepest part of the pond is exactly how a system is supposed to be installed.
3) A properly designed and installed bottom aeration system will show minimal water temp change from top to bottom, and will also show minimal O2 differences from top to bottom. That is the purpose of a bottom diffusion aeration system.
4) When installing a bottom diffusion aeration system in a pond that has a thermocline set up, with a very low DO reading at the bottom, it is critical to use the correct start-up procedure to prevent a fish kill. You WILL kill the fish in the pond if you just turn the system on and walk away. It's not the low O2 water that is killing the fish, it's the H2S gas that is killing the fish.
![[Linked Image from lh6.ggpht.com]](https://lh6.ggpht.com/_6_-SgakQ9co/S3Nx1jGAJWI/AAAAAAAABKU/DJIy4ZnF1t0/s800/I_subscribe.jpg)
