Algae in Shade Areas

[Alex M]

During winter & spring there are certain areas of the pool (one entire side) that is always in the shade. By early spring these areas get a green algae that continues to return even after treatment. The algae is 100% ONLY in the shaded areas. In the summer, once the entire pool gets sun, the algae does not return. I use a salt chlorinator and chlorine levels are fine and other levels seem to be ok.

[chem geek]

You can either brush the sides (to get the algae into the water so it will circulate into the SWG cell and die) or raise your Free Chlorine (FC) level a little. For an SWG pool, you usually need to keep your FC level at least at a minimum of 4.5% of the Cyanuric Acid (CYA) level. If your CYA is in the 60-80 ppm range but you have your FC in the 1-2 ppm range, then that is too low. The manufacturer recommendations of 1-3 for FC and 60-80 for CYA are wrong. We've seen plenty of pools with 1-2 ppm FC that get algae.

If your pool is high in phosphates (around 3000 ppb or higher) then an even higher FC level may be needed unless you want to use an algaecide (PolyQuat 60 or a phosphate remover).

Richard