A gray spot has appeared in the bottom of my well kept inground pool. It is spreading. How do I eliminate?

The pool is 6 yrs. old inground w/liner. I keep the water clean and balanced and test it several times a week. The "spot" was small at first, but has grown quite large. I use chemicals recommended by my pool people, but nothing changes the spot. I have no idea what it is or what caused it. Your help appreciated.

Answers:
There is a mysterious gray spotting that occurs in inground vinyl pools. Currently it is being investigated by a committee from the National Spa and Pool Institute (NSPI). Or at least it was when I retired. No determinations had been made at that time, however. They were trying to find out if it was a soil borne fungus that leached through the liner, or a mineral problem in the soil. Or something else. Sorry, I can't be more definitive on it, but I retired before the study was completed. You might check their website and see if it has a Q&A section. Good luck.

Other answers:
Maybe you need a new pool
Maybe you need a new pool
It is probably just a spot from the minerals in your water, I have the same thing happen on occasion. I would recommend a product called the Inground Pool Stain Eraser (for vinyl), which I have used quite successfully in the past.
You may have a water leak in the liner. Have a pool company check out the liner and determine if it is some kind of algea or a leak.
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