It's really kind of hard to tell much without water testing results. Post those when you get them and we'll take a look. Consider getting yourself a good test kit instead of relying on a pool store to test for you. We like the Taylor K-2006 or 2006C which is the same kit with larger quantities of some of the reagents. Click on the Amazon link in my signature. If you order through that link, the Pool Forum makes a little money on the sale which helps keep the forum online. Only buy if the seller is Amato Industries as some other sellers are substituting the K-2005 which you do NOT want.

It isn't necessary to change the sand. I'm on my 11th season with mine and some people are going much longer with theirs than I am.

Re-post with readings and we'll go from there. Welcome to the forum!