How deep is the pond, and is your home made diffuser in the deepest part? If not, how far is it below the surface?

Bubbles at the surface just means that there's air going thru it, not necessarily that it's "working".

The only way to tell if it's working is if you can test for dissolved O2 at that depth. You can get an idea by temperature differentiation from top water to bottom water, but the best way to tell is by actually checking for dissolved oxygen levels.

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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).