I may get corrected for this but I don't see a problem with having them on the bottom as long as you have something under them. I fasten my diffusers to garbage can lids and if neccessary attach bricks to weight them down. I set mine by attached a long nylon rope and pulling them in postion with the air on to see where they are lcoated. Leaving the air on seems to keep them from flipping over too. Anybody else?

Sounds to me like you brought up some nasty oxygen robbing sediment by laying the stones in the muck.

As far as springs are concerned many don't realize ground water has little or no oxygen in it when if first comes out of the ground. Therefore just because you have springs on the bottom does not mean your trout will do well. The temps may be low enough, but may be quite anoxic -- at least at first. And depending on the how much spring flow, the cooler temps can be nullified by surrounding warmer water.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.