Cause of Dark Discoloration on edges of fiberglass pool step?


Bronze Supporter
Jul 9, 2018
Columbus Grove, OH
Pool Size
Salt Water Generator
SWG Type
Pentair iChlor 30
This season we have noticed some darker discoloration on the edges of the steps in our fiberglass pool.
The attached picture makes it look a little darker than they appear, but they are there, nonetheless. I assume it is the edges getting darker and not the rest of the surface getting whiter, but it is tough to tell as it has been gradual. Brushing or trying to see if anything comes off with my fingernail either on the dark or lighter parts doesn't do anything.

Our pool chemistry has been very consistent this year after working out some issues with the SWG and filter early in the season. The only thing I have to constantly work on is bringing down the TA. The fill water from our well is not great because we have heavy sulfur, but there are no metals in it. Would high TA cause something like that, or should I be thinking of other culprits?
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