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biggest difference will be most of your pressurized spa systems will have a small skimmer on the other sideusally one and half inch hole, or 2 inch hole, water goes thru this then thru the pump and heater to the filter and back into the spa, Contaminents, body oils scum, not filteres first. on the others were the filter is in the main vessel of water -they usually skim the top of the water with a floating skimmer weir, then the through the pumps and heater...imo i will take the filter in the main body....