Hello, I have been SLAMming my pool for at least a week now. The water and walls/bottom have cleared up nicely except for one spot. It is about 1.5 feet below the deep-end return, and it looks yellowish/brownish to me. I've been brushing the pool, including this area, during the SLAM, and I haven't seen any noticeable changes in this particular spot. Photo below.
I don't know if this is algae or maybe a discoloration of the fiberglass coating. The fiberglass is discolored in multiple places. I don't remember all the places it's discolored. I vaguely remember this area was discolored but thought the discoloration was lighter. I may not be remembering correctly, and this is adding to my inability to determine if it's algae or discoloration.
Suggestions on what I should do next? (Note that I have not done an overnight chlorine loss test yet.)
Thank you.

I don't know if this is algae or maybe a discoloration of the fiberglass coating. The fiberglass is discolored in multiple places. I don't remember all the places it's discolored. I vaguely remember this area was discolored but thought the discoloration was lighter. I may not be remembering correctly, and this is adding to my inability to determine if it's algae or discoloration.
Suggestions on what I should do next? (Note that I have not done an overnight chlorine loss test yet.)
Thank you.
