Brown, dusty algae

[cynlys]

Thanks for help, I think

[chem geek]

If you have mustard/yellow algae, then with your 46 ppm CYA level it will take shocking with Free Chlorine at 25 ppm (after first lowering your pH to 7.2 using Muriatic Acid before you add the chlorine) and holding this chlorine level until there is no drop in FC overnight and/or a full week. See this thread for ideas on how to determine if this is really mustard/yellow algae or if it is pollen or dirt that is getting regularly blown in.

Richard