Dealing with mustard algae

[ In-progress and not complete ]

Mustard algae tends to be very chlorine resistant, and tends to reoccur. Most algaecides are ineffective against it. There are several options, but most have undesirable side effects.

Very high levels of chlorine, typically 30 - 50% of your stabilizer level. (If your stabilizer level is 60 ppm, you'd probably need 20 ppm to get rid of mustard.)

Contrary to what many think, you CAN swim with chlorine this high, but it is hard on swimsuits and may dry your skin. This method REQUIRES the use of the K2006 (or other DPD-FAS kit) in order accurately measure CYA and chlorine levels.

Heavy duty application of high concentration copper algaecide.

The problem with copper is green, greenish-blue, or bluish-green: copper stains pools and hair, and sometimes, fingernails. Less commonly, black stains can occur. If you don't mind stains, and if all swimmers have dark hair, this may be an option. Swimming during treatment is permitted, as long as green hair is not a problem.

Monochloramine, produced in your pool by raising the pH, adding products like Yellow OUT, and then 'shocking' the pool.

But monochloramine is VERY irritating to people, and is somewhat hard to remove. I do NOT recommend this approach. The pool must be closed during treatment, and often for several days after.

Low levels of phosphate (< PO4) + high levels of chlorine (15% of your CYA level)

With this options, chlorine effects on swimmers and swim suits will be unnoticeable to most swimmers, and there will be no need to close the pool during treatment. Maintaining low phosphates AFTER the algae is gone, plus maintaining normal chlorine levels (5 - 10% of the CYA level) will likely avoid any recurrence of the algae.

Currently, this is the option I'm testing locally and am most hopeful about. You do have to use another testkit, and you have something else to buy, but the cost has been lower than I expected and the result -- so far -- has been better. This is the only option that has no bad side effects on pool users.

If you want to go with the low phosphate option, you'll need the Taylor phosphate kit and phosphate remover:
Taylor K-1106 Phosphate Test Kit
Orenda PR-10000 Phosphate Remover
But, if you are going to pursue this, buy 2 quarts per 10k gallons in your pool to start. Get 3 if you plan to maintain low PO4 all season (recommended).

Using phosphate removers correctinly is a PROCESS, not a 1-step addition. It works VERY well, but ONLY if you do it right. Most people don't, and pool stores don't help.

Remember, low phosphates do NOT kill algae; it just makes the algae grow more slowly. This, in turn, makes the algae more susceptible to chlorine.

High levels of borates Borate levels greater than 60 ppm inhibit algae. The effect is not as strong with mustard algae as with other forms, but there is some effect. In addition, many users report that pool water with high levels of borates both look and feel noticeably better.

Unlike the other steps above, adding borates to your pool water is low maintenance and nearly permanent, since borates leave only when water is removed from the pool by splashing or draining; loss by evaporation has no effect on borate levels.

Borates can be added by using borax (sodium tetraborate decahydrate) or Proteam Optimizer (sodium tetraborate pentahydrate) PLUS muriatic acid. Or, boric acid (Optimizer Plus) can be added alone.

No matter which way you go, you need to manage your pool chemistry accurately, which is why we recommend the Taylor K2006 kit, found on the test kit info page.

I'm developing a vacation / mustard algae dosing spreadsheet. It is already usable; you can find it here: http://pool9.net/chart/mustard-dose/

.