Two things come to mind...


As Carl said...it sounds like they're trying to leave some weasel room in their warranty, should anything happen.

The second thing is that that builder/installer may have a working relationship with one (or more) pool stores in the area. It wouldn't surprise me if the pool builder has business cards at all the pool stores in the area. But it sure seems odd that he's laying these stipulations on his warranty. Especially when many of the pool store recommended chemicals come with consequences that effect another area of your pool water.

dan