My backyard pond turned green enough that I could barely see the fish. Here is the exact pump, 36W UV clarifier, DIY 5-gallon filter, 20-PPI foam, lava rock, bypass plumbing, mistakes, and before/after results from my real 1,200-gallon pond.
My 1,200-gallon pond stayed green until I added a 36W inline UV clarifier. Here is what changed, how I plumbed it, what flow rate mattered, and whether I would buy it again.