Not sure if this is the right forum to post this.
Pool Numbers as of this morning (pool opened on Saturday, 5/2):
pH = 7.2
TA = 75
Calcium = 140
CYA = 15 (added 8 lbs of powder CYA but not retested yet)
Over the last couple of years I've been noticing a dull yellow is stain on the liner. It has very defined edges as you can see in the attached photo. The photo doesn't make it appear as bad, but it is actually worse in real life. Very noticeable.
It doesn't brush off or even scrub off so I doubt it's algae. It's also happening on a steel bench in the deep end and on/around my steel stairs. Seems to be mostly around where there is steel from either the walls. Is something happening behind the liners with the steel? Any ideas to diagnose what the problem is? It just keeps getting more pronounced every year. This is the 8th season I've had the liner.