Not sure about the size of the pump or filter. I went out to look and I didn't see anything on the outside that would tell me but the filter holds 200 lbs of sand so maybe 21" The pool is 27ft round.
When I cleaned the filter I just used the liquid cleaner you pour in the skimmer & backwash out so I didn't look for any cracks, if there is any would they be visible on the outside? Yes, we are using filter sand.
I know this isn't alot to go on but thanks for your help!