OK, I have NO idea why he says 20lbs is bad. Sand filter?
Your pressure gauge isn't the problem. Either your filter is clogged or you have a restriction somewhere, or it's really too small for your pump. Have you changed pumps recently?
A sand filter may have gummed-up sand, or broken laterals. DE filters may have hard crusting on the screens. Cartridges may be clogged beyond what hosing-off will clean.