black spots in pool

[frankando]

Hello, my name is Frank and this is the first time posting to TFP. Need help with black spots throughout pool. it is a SWG pool approximately 10K gallons.
I don't know if its metals or algae. just had the water tested at my local pool store.
TC 4 PPM
FC 4 PPM
pH 7.8
TA 100 PPM
CA 400 PPM
Stabilizer 65 PPM
Total dissolved solids 4700
Salt 3400 PPM
I tried ascorbic acid in a sock overnight, pump off, and it left a brown streak following the slope of the poll.
Tried a chlorine tab, again overnight and it seemed to remove some spots. Not sure what to do next.
Pool located in SW Florida.

 

[JamesW]

Probably copper.

Black Algae Nightmare

Hello all: I purchased this home with an unground pool about a month ago. It had black staining along the walls and floors of the deep end which I now believe to be black algae. The pool is an unground Gunnite Pool. I have done the following: Scrubbed twice daily with a metal brush...

www.troublefreepool.com