In a nutrient rich pond, I've had white PVC coated within a week, and that was without roughing it up. It was all brown and you couldn't tell it was white.

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[Linked Image from lh6.ggpht.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).