Our pool is eight years old. About a year or so after construction, we started seeing a greyish spot on the bottom that slowly started spreading I have posted a picture of what it looks like now. I have read about "mottling" and the causes, but it looks and sounds like issues with concrete and troweling would have started showing soon after it was filled - not a year or two later. I do know that my husband did have issues with chemical balancing a couple of years ago and it seemed to get worse then - but it has continued to "grow" over the last couple of years . The pool chemicals are in check now - although we do have some black spots after winter which we are following directions to remove them - wire brush, brush X2/day and super chlorinate, etc.
So, I guess we are trying to determine what the cause of the mottling is and if it can be removed or treated? Or, is it going to require refinishing.
in-ground pool with spa and spillover