White Stains

[Curbweight]

Hello. New to forum.

Getting ready to close my pool this weekend, but within the last few days I've gotten white spots on the bottom of the pool about 4-5 inches in size. They do not brush away.
Don't know what these are. Have had metal staining over the season, but took care of that with metal out.
I am concerned that if I let this go, it may become a bigger problem. Any ideas?

FC-3
PH-7.5
TA-110
CH-300
CYA-50

Light Blue fiberglass pool

 

[JohnT]

Do you use powdered shock or powdered pH adjusters? They can stick to the bottom and be pretty difficult to remove. Your chemistry sounds good. Are the spots in a specific area?

 

[Curbweight]

Thanks for the response!

I did use Chlor Brite about 10 days ago, but felt I swept the bottom pretty well. I have used PH adjusters earlier in the season, but not within the last few months.
Spots are on the bottom only, in random places, both deep and shallow.