No, koi won't help. Well, I take that back. They might help by stirring up the water, making the pond muddier, therefore cutting down the light that reaches the pond bottom, which will reduce the weed growth.

There are other, better ways to reduce sunlight penetration. wink

www.hoosierpondpros.com

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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).