I have had a yellow / brownish spot near my main drain in my pool. The spot has been there for about two years before I knew about TFP. I did not think much of it in the past since I did overnight loss test and only lost about 0.5 on my FC.
What is the best way to determine what kind of spot I have? Sorry I did not include pictures but as soon as possible I can post. I have had proper FC levels for the past two years. Could it be mustard algae and what does it look like?
FC 20.0 (currently shocking pool)
Any help is appreciated.