I have my diffusers a bit off the bottom on weighted milk crates with no bottom plate so they do pull water from below. I initially had some discoloration from muck being sucked up by the plume but it wasn't too bad. That didn't last too long though and the water is no longer discolored so I think I'm good on that point.
I changed the timing on my setup a bit last night by adding a 2nd timer - actually a power strip with a built-in timer. It has 4 timed outlet and 4 always on. I now have the fountain turn off at dusk and back on at dawn. The diffusers run for 6 hours stating at 1 am and use all the air so I'll keep an eye out for bubbles on the rocks and cut it back if I see any.
My water is essentially clear at this point but it has the color of tea. I'm guessing it's from the tannin due to all the leaves collected over the years along with the field runoff. Would love to come up with a cost effective way to deal with it.
My setup is almost identical to yours, but I'm two crates high under the diffuser with no plate, so I'm 22" off the bottom. After a 6 hour run, like QA, my water is slightly murky, but still 16" minimum visibility which clears more by afternoon.
I used to have tannic colored water, but now, even after a week of rain, it stays olive green and the minimum visibility doesn't change.
