Thanks for the clarification Bill!

I suppose I was trying to convey that fountains do not oxygenate the entire water column if the pump intake is close to the surface, where the bottom diffusers have a better chance.

A pond that has DO throughout the water column, due to aeration, will have a larger carrying capacity and may have a fish population to match. If the bottom diffuser's run time was reduced, it could have a large impact on the health of the fish.

Is it safe to say that shutting fountains down (given that the intakes are shallow) would have much less impact, possibly no impact?

Fish on!,
Noel