Tony:

You try dawn dish soap and hot water?

F&C, leave the ball valve open too. If it't outside and in the sun, any solar heating will set up a convection current and move more air.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).