Here's a new one for me -- suddenly the pressure in my DE filter has dropped, pretty dramatically.

It is always around 40psi (and when it gets dirty it goes to 50 and I know it's time to clean) but today I looked and it went to 20psi. The rest of the system seems to be functioning fine (although my salt chorinator says "low amps" but I suspect this is a separate issue) and I have no idea how to or even if I should fix this (cleaning the filter wouldn't make the pressure go up, right?).

Any ideas? Or should I not worry?