Variable Speed pump "sizing" and how do I figure it out

[BigDave]

The label I read is actually attached to the wet end not the motor - FWIW.

[kelemvor]

So I think this is the right pump for me, and I'm still reading docs from "pump ed 101". If I understand Mark's Hydraulics 101, I should get ~78gpm with this pump on maximum given the 2" suction and 1.5" return in the spa. ~86GPM on high when running the pool (2" pipe both ways).. The Filter I'm looking at is Hayward DE7220 which lists a max flow rate of 150GPM so I should be good there as well, right?

I think my only concern is the Hydraulics 101 post mentions "Cartridge Filters: Most energy efficient and don't require backwashing. Best suited for areas with water restriction, high electrical rates and/or pools that use a SWG."

I use a SWG, how does that play into filter selection? Is it just a matter of the additional head loss created by the SWG or is there something else to consider?

[mas985]

With a SWG, you need to maintain salt and CYA levels in the water. Backwashing will remove both of these elements which will need to be replaced. A large DE filter is not as bad so you won't be replacing salt and CYA as much as you would a sand filter. Also, when you are backwashing, keep in mind that the salt level of the water is higher than normal so you may not want to backwash on to your lawn or landscaping. But if you have a backwash drain to the sewer system, this will not be a problem.