Pool Filter Pressure Very Low

I just opened my pool for its 4th season (23K gal gunite). I have a PacFab Clean and Clear Plus Cartridge filter system.
The water was pretty gunked up at opening. When I started the pump up it was reading 10psi (which is a very normal reading). A few hours later it was up to almost 20psi (again normal because the filters got gummed up). I took the filters out and cleaned them. But now, the pressure reads about 1-2 psi.
Something seems very wrong. The pool is filled to the top and there is no air in the system. It doesn't matter if I set the value to Skimmer or Main drain - the reading stays the same.
Water coming out of the jets feels like its coming out at the normal rate.
Any idea what might be going on? Perhaps the gauge suddenly went bad? The needle does "jump" up and down a few psi when I first start the system - does this jumpiness (not a smooth motion) indicate a bad gauge?
Thanx in advance.
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Lex writes:

Commonly happens. They never last. They're cheap. Buy one to test with, keep as a spare if it isn't the trouble.
Your hand over the outlet is less precise, but more reliable, as a flow meter.
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The gauge may have failed, they frequently do. But, it may also be that the gasket in the backwash valve moved when you operated it so water is being pumped out of the pool and right back into the pool. In this case only a small amount of the water is actually being filtered.
RB
Lex wrote:

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