Yellow/Brown dusty deposits that reappear repeatedly

[chem geek]

I've had my cl levels at about 30 for 3 days now. pump on 24 hours/day.

Pool is definately clearing up.

An FC of 30 with a CYA of 40 (that you mentioned in an earlier post) is a disinfecting chlorine (HOCl) level of around 1.3 ppm (an FC of 25 is an HOCl level of around 0.8 ppm) so it looks like we are narrowing down the amount of chlorine needed to kill this stuff to be a minimum of at least the column of 1 ppm in this table. If others have this problem with different levels of CYA (especially higher), then we can confirm this and eventually update Ben's Best Guess CYA chart to have at least two shock columns -- one for plain green algae (probably a 0.3 ppm level) and another for this mustard/yellow algae (probably a 1 ppm level). That leaves black algae where others have written about rubbing Tri-Chlor pucks on the algae, but I'm not sure about what overall pool chlorine levels are used at the same time to be effective.

Thank you all for keeping track of your chlorine (FC) and CYA levels during your battles with this algae. I know that the chemistry of what's going on is the last thing to enter your minds, but this information will ultimately help others.

Richard