I'm converting my DE filter to sand and thinking about a Hayward Pro-series side mount and was getting conflicting sizes, so I wanted to get your opinions as to the right size. My pool size is about 21k gallons with a 1.5 hp pump, 2" plumbing in and 1 1/2" out. I currently have a 48 sqft DE filter. My first size suggestion came from Leslie's which said I needed at least a S310S, but after reviewing Hayward's pump and filter sizing worksheet (I estimated about 63 total dynamic head and desired flow of about 50 GPM, assuming my values are correct), it seems that S244S or even possible a S210S would work. Given my limited pad size and the considerable increase in $$$ between the S310S and others, I don't want to get more that is needed. My question is which would be best for me (I hope I have given enough info, if not let me know)?
Model # Sand (lbs) Filtration Area Design Flow 8 hour 10 hour
S210S 200 2.20 ft2 44 GPM 21120 26400
S244S 300 3.14 62 29760 37200
S310S 500 4.91 98 47040 58800