Happy spring! As I sit here isolating, my thoughts are expectant for summer and … the pool. Last two years I've had a persistent mustard algae problem (3 years ago I broke my wrist in the fall and fell down on many jobs, the pool being one of them). That year and the next, I followed all the shock and super-shock rules and super-cleaning and this past year I pretty much got it under control -- as long as I kept FC up to 6. Before the MA scourge hit my normal was 3-5ppm. And let me say that I'm a minimalist per TFP and it has worked wonderfully, until the MA appeared. At closing I clean and slam, and then close at about 8 or 9ppm. Every spring I open it to a clean pool -- looks like maybe I haven't vacuumed in a couple of weeks! Last year I used chlorine (liquid 10%) religiously and baking soda once or twice, and that was it. Very stable chemistry. A couple of times I got brave and let the FC drift down to 5 and in a few days, here'd come the mustard algae again. I'd clean and brush and slam at the first sight of it, and all was well, as long as FC didn't drop below 6. The guy who takes care of my pool when I'm away, formerly a pool pro in Florida, tells me I'm degrading my liner by keeping it that high. Last fall I was reading the forums and some external articles and became convinced I should add Polyquat to my chems. Advice, please, and thank you.