It's a 27" Waterway Millennium. Called the Pool store where I bought the pool and they said 350 lbs. so 7 50# bags later here we are. I've had the same setup since we bought the pool 5 years ago. Don't remember going through all this the first year or two but the last few it has taken forever to clear up, that's why i thought the sand was bad and changed it. I had the same problem last year, it took weeks and weeks to clear up but when it finally did, the water was crystal clear for the whole summer. I guess I will call the store and see if they carry DE, anything else I can use to do the test if they don't have any?