We've seen several cases of VERY chlorine resistant algae in the last month. There are X options:

1. Hold chlorine levels at 25 - 30 ppm for several days. (No side effects, except increased chlorine use.)
2. Raise borates to 60 ppm. (All side effects are positive; semi-permanent additive. Reduces algae; does not eliminate it.)
3. Use sodium bromide (May not be effective; can increase chlorine use for weeks after.)
4. Use ammonium sulfate or chloride to make monochloramine. (Makes pool unusable for several days; may result in algae rebound after a couple of weeks.)
5. Use polyquat, after allowing chlorine to drop below 10 ppm. (Slightly increased chlorine consumption; improved water clarity; may not be effective.)

Please note that the ONLY choice that I know from my own experience will rapidly kill mustard algae is #4, monochloramine. But, I do NOT recommend it -- it makes a mess of your pool, and in my experience, pools on which I used it seemed MORE likely to have algae problems later.

What I'd recommend is borates. 60 ppm of borates are a good winterizing prep, and will still be there next spring, minus whatever water you drain. Using borates makes the pool MORE, not less, pleasant for swimming. But it's up to you: you can simply raise the chlorine level till the mustard algae dies.

REGARDLESS of your approach, you need to brush, except with the monochloramine option (#4 - Yellow Out, Green to Clean, Mustard Master, etc.)

If you want to go with the borax option, I'd suggest ordering this:
Granular Boric Acid, 55 lb @ Amazon => $117 (2.13/lb)[/INDENT]and this
Lamote Borate test strips

Because the boric acid will lower the pH, you'll need to add borax to compensate; both will increase your borate level. More info here: http://www.poolforum.com/pf2/showthread.php?18597