Sound like the laterals are wearing out these are the spokes at the bottom of the sand filter after time they wear out and don't stop the sand any more they will need replacing.
how do you clean jacuzzi sand filter, and replace sand
distinguish between slow and rapid sand filter
Nothing if its a sand filter However if sand is coming into the pool from the filter then you may have to replace one ore more laterals in the sand filter as they have worn and are letting sand through to the pool,
Do you mean how do you install a sand filter?.
differentiate between slow and rapid sand filters
If you have a sand filter the laterals in it may be starting to show signs of wear these wil blow sand from the sand filter into the pool when they wear out.
Your filter will tell you on the side of it how much media sand to put in it.
If you are getting sand coming into the pool and have a sand filter you may have to replace worn laterals in the sand filter.
My Hayward sand filter doesn't have a liner. I just add the sand to the pressure vessel.
A 300-gallon filter? I have no clue. The industry rates filter on the diameter of the filter tank. So if you can cover the gallons to inches I can tell you how much sand you will need.
NO
Sand is an extremely efficient filter for anything