Mustard algae - which is usually a yellowish-green or brown colour, attaches itself to pool walls and other items, including equipment and pool toys. Unfortunately, since it is chlorine resistant, special care and steps must be followed to properly remove this pesky algae from your pool.
Follow these steps to properly remove mustard algae from your pool:
1. Remove all items from your pool (including steps, toys, cleaners, etc) and clean each item thoroughly clean steps, toys and accessories outside of the pool to ensure no mustard algae remains stuck to them
2. Using a pool brush, scrub the algae off the sides of your pool walls and also off of the pool floor; once all of the algae has settled on the bottom, run your manual vacuum though your skimmer on "waste mode" (be sure your filter is set to waste, so the mustard algae bypasses your sand) or open your drain port on the cartridge filter and remove the cartridges inside.
3. Re-balance your pH and alkalinity levels, ensuring pH levels are between 7.2 and 7.4, and that alkalinity levels are between 80 and 120 ppm; balanced water will help shock work more quickly and effectively - use test strips to check your water chemistry
4. Shock your pool, using twice the amount of a typical shock treatment, brushing any residual algae aggressively to prevent any remaining spores from continuing to grow. This process may need to be repeated every 24 hrs depending on the amount of algae present within the pool.
5. Run your pool pump continuously until all algae is gone and chlorine levels have dissipated
6. Backwash your sand filter, or clean your cartridge filters to ensure any residual algae spores caught during the continuous run cycle have been removed; if any algae is still present in the pool afterwards, shock the pool again - for pool owners with a sand filter, a sand change may be required
7. Your pool may have residual dead matter from the mustard algae remaining. Vacuum your pool on "waste mode" using your manual cleaner, until all of the algae has been filtered out of the pool; or use an enzyme product such as Pool First Aid to remove the dead algae matter (highly recommended)
8. Treat your pool water with algaecide, and continue to monitor chemical balance closely for the next few days.