Mustard algae is a chlorine-resistant form of green algae that often resembles dirt or sand on bottom or sides of pool. It contains compounds that act as a defence mechanism against the oxidation efforts of sanitizers, helping it survive even in highly chlorinated conditions. This factor can even create a large chlorine demand in certain situations. Mustard algae can be brushed away very easily, but returns quickly.

• Use MSA II as it kills all types of swimming pool algae and resistant algae

1. Maintain a sanitizer residual of 1-3ppm
2. Do an initial and weekly application of a preventative algaecide (such as BACK UP Algae Inhibitor)
3. Shock routinely
4. Make sure there is adequate circulation and filtration
5. Brushing surfaces is vital