Check the fountain mfg's to see what materials are used to build them. Otterbine uses stainless steel, I've seek Kasco with both aluminum and plastic impellers. Never saw a Scott unit.

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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).