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Yes, the trees will contribute a lot to the high P levels. Leaves in the water decomposing.

Raking algae out, removing some trees to minimize leaves in the pond, adding Tilapia every year, etc., etc.

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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).