Mustard Algae???

[chem geek]

Users of this forum have found that it takes a lot more chlorine to kill the mustard/yellow algae than it does for the more common green algae. This chart shows the amount of Free Chlorine (FC) needed to achieve the desired level of disinfecting chlorine (HOCl at the top of each column) at various levels of CYA. To kill mustard/yellow algae, it takes about 1.0 ppm disinfecting chlorine so that would be at least 21 ppm FC with your 30 ppm CYA (more common green algae only needs no more than 0.3 ppm disinfecting chlorine). The advise of using 25 ppm FC is good. In addition, I would lower your pH to at least 7.2 (but not lower than 7.0) before adding the chlorine since the chlorine will raise the pH and make the chlorine less effective.

Then, it's patience, patience, patience.

Richard