In .com,
Scott Townsend typed:
So with this heat we have had here in Sunny CA, it seems like
there
are more and more of these maybe 2" around little bubble like
things
on the bottom of the shallow end (3.5'-4.5') of the pool. Last
year
there were a few, 6 maybe, now I'm up to 20+ of them. You
cannot
press them down, so they do not seem to be flexible.

What are they?
What causes Them?
What should I do about them?

Thanks,
Scott-

Sounds like delamination; incorrect install or bad material.
Check your warranty and make some calls.