20 sf bait tank ?

[Blue_Heron]

...but if your anchored do you meen you have no flow and the water enter from the transome drain hole ?
Perhaps that why on mine someone had a airator pump

At rest, the waterline as just above the deck. The pump keeps the water level about 3" below the deck. Even with only 3" of hydrostatic head, the water flows in through the transom pretty well. And you don't really need water flow when you're on plane. The water sloshes around enough to aerate it.
Dave