After 2 weeks of high heat (over 100 degrees), my pool is showing its first ever infestation of mustard algae. The pool water was at 88-91 degrees during the heat and has finally dropped to a reasonable 82 degrees, which is pretty standard for this time of year.

I keep brushing the sides down, but the algae keeps coming back. Here are my levels:

Free chlorine = 4.2ppm
total chlorine = 4.6ppm
Combined chlorine = 0.3ppm
pH = 7.8
Hardness = 240ppm
alkalinity = 88 ppm
cya = 75ppm
copper = 0.1ppm
Iron = 0.3ppm

I was told by the pool store (and this is one that doesn't try to sell you stuff - they're actually honest & helpful) that my chlorine is too high and may be part of the problem. I added - at their suggestion - a non chlorine shock and some polyquat algaecide.

Forgot to say this is an inground plaster pool of 30k gallons, sand filter.

Any comments or suggestions would be appreciated...