Without the air running, you might have had the DO levels drop at a more shallow depth. For example at 5' instead of at 7'.

So even though you are not getting good levels all the way to the bottom, you likely are getting many more gallons of water oxygenated for the fish to live in.

The diffusers are moving x gallons of water from the lower regions to the surface to reach oxygen. It might take multiples of x to enrich the water all the way to the bottom.


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