Hi Spbb . . .

1. Some pools are more prone to mustard algae than others, but I don't know why.

2. High CYA is *usually*, but not always, a contributing factor.

3. High chlorine will kill mustard algae, but with the CYA levels over 100 ppm, it will take extremely high chlorine levels -- higher than 20 ppm. Read the Best Guess page linked in my signature.

4. Polyquat is not, in my experience, very effective against mustard algae. Copper can be, but at the price of stains and green hair.

5. Sufficiently high levels of borates (> 50 ppm) seems to inhibit mustard algae.

6. Very low levels of phosphates (> 125 ppb) probably weakens mustard algae significantly. I'm currently testing this, and seeing positive -- but not definitive -- results.

My recommendations for you:

1. Add large doses of bleach in the evening, after brushing. 2 gallons of 8% plain household bleach per 10K gallons of water.
2. Maintain chlorine levels above dark yellow via OTO testing, till your K1006 arrives.
3. Post your test results, as soon as you have the K2006. Then, let's decide what to do.