i see flat rocks maybe a 1/4 of an inch to a 1/2 an inch thick in the petstores that you buy by the pound and i was wondering if those were ok for salt water tanks because i know people usually use them for fresh water tanks so i was just wondering if they would affect the water in any way thanks for any info you can give me.

If you're talking about the polished pebbles they should be fine unless they are coated, and then the saltwater would wear away at them and possibly be dangerous.