Quote Originally Posted by PoolDoc View Post
Mustard algae is VERY easy to brush off -- but it's apparently hard to remove 100% since it tends to return to the same spots.

I'd just dose with 4 gallons of plain 6% household bleach AND 1 lb of dichlor each evening, till you get the reagent. And, brush your spots daily, preferably right after adding the chlorine.

(I'm sure that somewhere there's a pool store that sells Taylor FAS-DPD reagents, but I've never heard of one that did so.)
I actually found the FAS-DPD powder in a Leslies near White Plains. The clerk couldn't find a price anywhere in the system...and just gave it to me. That must be 10 years ago because it was just after my Dad passed away, in 2002. I was building my current pool and had taken down my Intex Donut for the last time.