I looked at the Pooltrine brand Polyquat and they recommend 16 oz per 10K gallons so for your 30K pool you would use 1.5 quarts so 2 quarts isn't way off.

As far as the chlorine, what do your latest test numbers look like?

Lastly, I don't know how well a clarifier works so I can't help you there.

If you look up mwsmith2, try to send him a PM - since he has dealt with mustard algae he should be able to give you good advice.

Peter