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Treating Mustard Algae


Mustard algae is a form of green algae that is highly resistant to chlorine. Special treatments must be used to eliminate it. Mustard algae is yellowish-green in color and often looks like dirt or sand on the bottom or sides of the pool. It brushes away very easily, but returns quickly. If left untreated, it can turn the entire pool a pea-green color in a very short time. Mustard algae will usually create a fairly large chlorine demand, although it can survive in high levels of chlorine. In SoftSwim® pools, mustard algae will consume SoftSwim® Clarifier.


The best plan is to prevent mustard algae from every forming. Following are some of the ways to help prevent it:
– Follow the BioGuard® 3 Step program of your choice as outlined in your BioGuard® Pool Care Guide.
– Keep the pH at 7.4 to 7.6.
– Clean the pool regularly, skimming, brushing, vacuuming and backwashing the filter as needed.
– Keep the filter clean and water circulating properly. Keep the skimmer and hair and lint baskets clean. Check them often if you have a lot of cotton from cotton wood trees or debris blowing in the air around the pool.
– Keep the pool water under 82 degrees.
– Keep the water properly balanced.
I- f you have been swimming in the ocean or a lake or a pool by the ocean or lake, you need to mix a solution of MSA Algicide and treat the suits. Or if you know someone who has mustard algae and you or your kids have been swimming in the pool, treat your suits with MSA Algicide and water.
– It is very important that you do not forget to oxidize with Burn Out® Extreme or Burn Out® 35 every 2 weeks. Use BioGuard® Smart ShockTM weekly at the rate of one pound per 12,000 gallons. Use BioGuard® Smart ShockTM weekly instead of Burn Out® Extreme or Burn Out® 35 to maintain a sparkling clean fresh pool. The advantage of using BioGuard® Smart ShockTM is weekly application and swimming may resume in 15 minutes. You need to oxidize swimmer wastes out of the water, like perspiration, urine, mucus discharges, hair oils, body creams, suntan lotions, etc. The next morning, add your maintenance dose of algicide.

Anytime you let the chlorine residual fall below 1.0 ppm, it is a good idea to add a granular chlorine like Super Soluable or Burn Out® Extreme (3-4 oz. per 10,000 gallons), or Burn Out® 35 (4-5 oz. per 10,000 gallons). If you haven’t oxidized for awhile, go ahead and oxidize (preferably at night.)

Additional applications of BioGuard® Smart ShockTM may be added after periods of extremely heavy pool useage, significant rainfall or the appearance of cloudy water.

Apply additional treatments at the rate of one pound of BioGuard® Smart ShockTM for 12,000 gallons of water.

If you or someone in your neighborhood fertilizes with any type of fertilizer, you may want to check your chlorine residual. If it is low, oxidize with normal amounts of oxidizer. The fertilizer has nitrogen which creates chloramines and a deficit in chlorine.

Always check chlorine residual after rain storms. After severe storms when chlorine is low you want to shock and you always want to add a maintenance dose of algicide.


STEP 1: Adjust pH to 7.4. If pH is higher than 7.6 you can loose 20-30% chlorine efficiency.
STEP 2: Brush floor and walls. Let settle and vacuum and backwash filter.
STEP 3: Oxidize with 1 lb. of Burn Out® Extreme per 6,000 gallons of water OR 1 lb. of Burn Out® 35 per 6,000 gallons of water. Preferably at night with the pump running. (Amount of oxidizer may vary with condition of pool water.) Be sure to keep your chlorine level at a 3.0 ppm or above during the entire treatment.
STEP 4: One hour later add 8 ounces of MSA Algicide per 10,000 gallons of water. Dilute the concentrate in a bucket of water and apply in areas of greatest circulation.
STEP 5: Put all cleaning equipment and toys in the pool to kill the algae on them. These spores are ambient and will survive dehydration. Take a bucket of water, and small amount of MSA, dip your bathing suits in treated water. These spores can survive the washing machine. Anyone that has been swimming in the ocean or a lake needs to treat their suits with a MSA solution. Rinse the deck off with a garden hose.
STEP 6: One to two days later, vacuum to waste if your filter has the option. When you vacuum to waste, have the garden hose running in the skimmer at the same time. If you cannot vacuum to waste, Sparkle-Up® will help trap this algae in the filter so it can be backwashed out.
STEP 7: Thirty-six hours to one week later, when all the algae is gone, Test for residual of copper. If copper is present, treat with Pool Magnet Plus® Scale Inhibitor or Metal Magic® to tie up the copper from the MSA algicide. Sparkle-Up® will help remove the metal.
STEP 8: It is always a good idea to clean the filter with Strip Kwik. The filter can be an excellent breeding ground for algae and bacteria.
STEP 9: If not using algicide on a regular basis, use one quart of Back-Up or Algae All 60 per 25,000 gallons of water. Add next day after using MSA.
STEP 10: If the algae still persist, then a second treatment may be needed. If the pool has been treated two or more times with MSA you may want to treat with Proteam Mustard & Black Magic®.


In SoftSwim pools, follow the steps below:
STEP 1: With pump running, apply an initial dose of Algae All 60. (Note: Use of Algae All 60 will interfere with SoftSwim B® readings for approximately three (3) weeks).
STEP 2: Apply two (2) gallons of SoftSwim C® per 10,000 gallons.
STEP 3: Apply an initial dose of SoftSwim A®.
STEP 4: Chemically clean the filter with SoftSwim Filter Cleaner.

After clearing mustard algae, chemically clean the filter and follow an aggressive maintenance program for a few weeks. Use algicide weekly and increase the dosage a few ounces. Keep sanitizer levels toward the higher end of the scale (chlorine — 3-5 ppm, bromine — 4-6 ppm, SoftSwim — 50 ppm). Shock more frequently. Brush the pool once a week.

Download a printable PDF: BUL-118 – MUSTARD ALGAE

NOTE: Always follow label directions and manufacturer’s instructions for each product used. Conditions may vary from pool to pool. Ultra Modern Pool & Patio does not assume any responsibility or liability for the results that may be obtained through utilization of this or any other program, procedure or product.

Bulletin #118