having to backwash new sand filter multiple times a week

[madwil]

20 seems a little high, but I don't think ridiculous...
Mine runs as low as 6 or 7, but I have a 70gpm sand filter (200 or 250 lb, I think) and my pump is rated at 75 gpm I think, so not much extra...
The 20 is the cumulative total of backpressure, mostly from the filter but also from the return lines; did you have to change any piping? and did you use the same size or bigger?

[PoolDoc]

Whoever sold you a 200# sand filter as a 70 GPM filter was deceiving you, either accidentally (because they were ignorant) or deliberately.

To get good results at 70GPM, you need at least a 30" filter -- 600# of sand. Even a 24" filter needs ~350# of sand.

To get definite answers, you need to post pump & filter maker and models, and send photos to poolforum AT gmail DOT com

[SalemCastles]

My Hayward 22" (250#) runs at 16 PSI with the skimmer and 14 PSI using the Navigator when clean. The Navigator stops working around 22 PSI. I always find that the Navigator causes the filter to get dirty much faster than the skimmer even when the pool looks clean and I run it under the solar cover most of the time. Did you initially run the filter in the backwash position? Hayward recommends you initially backwash for the first two minutes to flush any impurities and fine sand particles. Also are you rinsing after the backwash? This prevents flushed dirt from going back into the filter and pool.