if i can add to this one a bit..and all the advice is good so far..if the sand is hard, it's not going to filter anything ..or it may be partially hard..but to the point you don't want to go poking a stick in there as you could wreck the vanes inside..but you should be able to easily poke a finger around our 2 fingers and run sand between your fingers anywhere you can reach in the filter if it's good. i believe sand in filters is supposed to be good about 5 years..that maybe rated based on year round use as my sand is at least 7 years old and was still completely "sandy" consistency at the end of last season.