I am sure that I have mustard algae. It is a yellowish-green color and does brush off the walls easily. I can get rid of it by shocking heavily. A couple of weeks go by and there it is again. I have heard the copper algaecide will work, but I have a aggregate finished pool and would rather not use copper. Any other suggestions.

Your description can be that of mustard algae. It can be treated with other than copper algaecides. You might have a two-fold problem. One part is that your sanitizer level, chlorine I assume, is probably not being maintained adequately at all times. Make sure that you maintain a 1-3 PPM level of Free Chlorine, at all times. Do this and it is unlikely that you will see the mustard algae return. If the problems starts in certain areas, redirect the return flow to improve the water flow, in that area. Adding a circulation booster, such as “The Pool Circulator“, will improve the dispersal of chemicals and dramatically improve circulation. It’s simple to install. For more information, please click here. One of the best products to use for mustard algae is one of those “Yellow” Products containing sodium bromide. Used in conjunction with a shock treatment, it will generate bromine, which seems to be especially effective against mustard algae. It’s important to test for Free Chlorine, when shocking a pool. Make sure that you add enough product and it is added frequently enough to boost the Free Chlorine to 5-10 PPM. You want at least 1-3 PPM persisting through the over night period. Do that and there should a major reduction in the mustard algae, by the morning. Keep the filter operating continuously, until the problem is controlled. You didn’t mention if you have a robotic pool cleaner. They are very effective at cleaning and improving the water circulation on the bottom and can help remove some of the powdery mustard algae. Improving circulation, in the corners, will help prevent a recurrence.  If this website was helpful, in solving your problem, please consider joining our E-Letter Mailing List.  You’ll receive E-Letters, with helpful information, new product updates, suggestions and sale announcements. I hope that I have provided the solution.