I have read that the best way to get higher levels of oxygen in the water is by using a fountain or dropping the water back into the FT from the GBs leaving an air gap of 6 or more inches. If you look at most city reservoirs, this kind of backs up this claim, because they have a fountain in the middle of most reservoirs (and fish ponds in the state fish hatcheries) to add oxygen to the water, rather than air stones. What I read is that the water will not absorb the oxygen molecules from the air being pumped through the stones and up through a water column, as well as it will if the water is picking up oxygen from the air, and forcing it down onto the surface of the water from a fountain or stream (turbulence). These are not my words, ideas or experimentation, I know from nothin' about DO .... some geeky scientist wrote this stuff ... and I'm just quoting it from my bad memory. The water in a creek or river picks up oxygen from turbulence - bubbling brooks and raging rivers with the water running over the rocks and such are a real good example. I can't find it right at hand here, but I have a book on the cichlids (and Tilapia) of Lake Tanganyika and Lake Malawi and it states that in the lower regions of these lakes the fish are more oxygen deprived because there are no currents flowing nor winds blowing the deeper you go - another case for turbulence .

Just my 2 centavos .........