Swimming Pool Blog

Treatment of Yellow Algae in Pools

2010 Pool Drowning Statistics
by Rob Cox, September 19, 2010

Treatment of Yellow Algae in Pools


az pool care image of yellow algae on swimming pool floor


Also known as Mustard Algae, Yellow algae is a unique type of algae. The most distinctive distinction between other colors of algae - blue, blue-green, or black algae, is that Yellow algae finds a home in the uneven surfaces of your pool.

Pits or crevices in plaster, or dips and dirty areas on a pool liner create a safe harbor for this particular strain of pool algae. A weak, cowardly algae, it hides in the places that our cleaning equipment and sanitizers don't always reach effectively.

Many pool owners find yellow algae to be one of the more difficult strains of algae to control. This is due to it's ability to hide small cells of life, deep in a crack or buried sufficiently that it can escape complete chlorination. Yellow algae is not a very strong algae, nor is it hard to kill - it's just hard to kill all of it.

With proper techniques, you can effectively eradicate it.



Identifying Yellow Algae in a swimming pool:

1. Clinging, Hiding blooms, not Free-Floating.

2. Bright yellow to dark yellow mustard color.

3. Brushes off the wall fairly easily.

4. May prefer shady spots of your pool.

5. Found under ladder treads, behind pool lights, and inside pool filter.


Where does Yellow Algae come from?

Yellow algae is not a strain that is commonly found in pools, and in many cases the plant can be introduced to a pool in the swimsuits or hair of swimmers who were just enjoying the river or the ocean. We have also found that most pools with Yellow Algae contamination also had high levels of Nitrates in the pool water. Nitrates provide an excellent food source for all types of algae. Phosphates can also be contributing to growth of Yellow Algae in your pool. Read our earlier blog post on Phosphates and Nitrates in swimming pools.

How to Remove Yellow Algae from a Swimming Pool

1. Clean the Pool. Brush every spot of algae off, using a quality pool brush with stiff nylon or stainless steel bristles will give you the best success. If you don't own at least one good pool brush, this may be why you have algae in the first place! Pools need to be brushed regularly, and for algae removal, the action of brushing is extremely important. Brushing removes it from the surface or exposes vulnerable layers of the algae, so that the chlorine can do it's job. After brushing, vacuuming to waste, very slowly and carefully, all of the settled shock dust and dead algae cells. If you cannot vacuum to waste, vacuum into the filter, but do this before you have cleaned the filter (as below). Very important to vacuum out all dead algae cells, which can regenerate if left in the pool.

2. Bleach everything. Use a solution of 1 gallon of bleach per 5 gallons of water. Use a trash can for larger items. Soak for 5 minutes, then flip over to soak the upper half.  You can also soak your skimmer baskets and pump basket. If you have a pool cleaner, hoses, bags and other parts can also be bleach soaked for several minutes. Yellow algae likes to find a home underneath hose floats especially. Anything that goes into the pool could be contaminated. Floats, Noodles, Balls, maybe even you! Give everything a good bleaching, even your cleaning tools.

3. Use a Chlorine Accelerator. This is the preferred treatment for Yellow Algae. Not an algaecide, but a proprietary mixture (usually Sodium Bromide) that boosts the effectiveness of pool shock. Sold under many names such as Mustard Buster or Yellow Out or Yellow Treat, these chemicals are added to the pool at the same time as the shock (after balancing the water).

4. Use a Phosphate Remover chemical. As mentioned above, in our experience most pools with Yellow Algae blooms also test positive for Phosphates or Nitrates in the water. Removing the food source for the algae is just good solid warfare.

5. Clean the Filter. Cleaning of the filter media thoroughly is key to removing yellow algae from your pool. If you have a DE or a Cartridge filter, remove the filter from the tank, and clean thoroughly with a hose. Then soak in a pool filter cleaner product to remove oils and minerals. Rinse again. If your cartridge filter has other internal plastic parts, soak these also. The entire cartridge or grid assembly should be soaked in a chlorine solution as described above. For Sand Filters, use a Filter Cleaner product to remove oils and minerals from the sand. Then remove dome or valve top, and pour into the tank 5 gallons of a bleach solution. Allow it to soak for several hours.

In lieu of cleaning or bleaching the filter media thoroughly, one could replace the filter media instead. New filter sand or new cartridge or de filter grids would ensure that Yellow Algae is not harboring in our filter. Especially if the sand or cartridge is old (over 5 years), it may be time to replace anyway.