I don't know about the Gorilla Pad, etc..
But many many members here have used the pink foam board that was mention, with good results. There is one that's not waterproof though, you want to stay away from that, I believe it's white IIRC, you also have to tape it together and I think tape the cut edges.
Take a stroll through the search function and have a look, lots of threads on it.
If you can't find what you need and someone doesn't come along here to say what exact type of foam, and which one not to get, procedure, etc..
Then just start a new thread here in the AGP section, it's a separate topic enough, saving for the above, that I'd think it'd be OK. But do wait to see if someone comes along and answers your question.
As far as taking the pool down. NOOOOOoooooOOOO! Don't do that.
I know it's frustrating when things don't go according to plan, despite best efforts.
But you have already put far too much time, money & effort into it to do that.
You will more than recoup your loss on the pool by not ever being taken for a ride by the pool store, or paying a pool guy to take care of it for you, so long as you stick around this forum and learn to take care of it yourself. You will more than regain your investment in a very short time and be happily enjoying your pool for many years to come.
It's not unusual for many folks that visit the forums for the 1st time, to have spent $300-600 or more at the pool store. We call it getting Pool Stored.
A BBB'er will typically spend as little as $10-15/mo. to $30-40 or so. Bleach is the daily, every other day thing, borax is a one time thing or to fix a problem, so is baking soda. Muriatic acid, MA as we call it is once a month, once a season, or something in between, depending on one's pool. CYA, cyanuric acid or stabilizer is a once a season thing as well, or to top it off from splash out, drainage, leak, etc..
So there's just the initial price of those chemicals, use what you need, then store the rest for safe keeping until you need them again at some point, then just bleach as your pool requires it. All depending on bather load & size of pool, plus climate conditions and time of year.
Nothing is free of repairs and initial investment when something goes wrong. We're constantly fixing things here around the house, it's a never ending chore. But at least the pool is fun and enjoyable, not a necessity, like a hot water heater is when your groundwater is about 27deg F. YIKES!! Hard to take a shower in that, HAHA! It's like shock therapy /w out the electricity.
I like what PAGirl suggested, definitely a good idea. Could be sitting right on top of an ant hill or something right there in that one spot. That would explain the concentrated area.
Great idea PAGirl!!!
Hang in there Jett74, you're on your way to pool fun and armed for next season.