Mustard Algae in Winter - what's going on? Options?

New pool owner in the South and I struggled with Mustard Algae a bit this summer but a single dose of copper based algaecide got things under control and I had no further issues until I had to do a complete drain and refill for liner repairs at the end of Summer. Now I've been dealing with the stubborn algae again ever since. My water is perfectly clear there's just small patches of visible algae growing on the seams/bumps in the liner.

For background, I am a TFP adherent and maintain all chems in-line with the PoolMath app. Liquid chlorine only, PH is 7.4, CYA is 30, and use Taylor 2006 test kit to check levels at least bi-weekly.
I did the SLAM to mustard algae FC levels THREE times (I've put an insane amount of liquid chlorine into the pool lately) but the algae would keep showing up on the seams of liner and in low spots a few days to a week later. Yes, FC was maintained above Mustard Algae Shock level and OLCT was passed each time.

Finally, I gave in and used some copper algaecide.... mustard still came back.... did a 2nd dose.... mustard still came back. Tried some sodium bromide algaecide (Yellow treat), mustard still came back... did a 2nd dose... mustard still came back... WTF
I was hoping the cool water temps in Fall and Winter would stop it but it's been just the opposite.

Since the start of Nov, I don't think my FC has ever dropped below about 10ppm and I keep seeing algae. Test today showed 11ppm FC, 0ppm CC and there was still visible mustard algae along seams of liner. Water temps have been ~45-55F. I thought at these FC levels I wouldn't see any algae?

There are only 2 differences I can think of to explain this:

  • In the summer we use the pool literally every day for at least several hours. No one is using the pool in winter so there's a lot less agitation/movement of the water. And admittedly I brush about 1x a week max. In the summer, I was only brushing 1-2X a month and it looked great.
  • The big one: All summer, there was basically zero organic matter (other than people) in the pool. Aside from the initial mustard algae issue, it was always perfectly clean. Now in Fall/Winter, I am getting leaves, seeds, etc. dropped in the pool constantly. I empty skimmers at least 1x a day and vacuum several times a week, so things aren't left in there for long, but there's just A LOT more leaves and stuff entering the water.

I've tried so many things already, so any advice on how to stop this algae once and for all?

Brush more often? Try a phosphate remover?