Watermaker filters become fouled by virtue of what's in the water,
not as a result of time. Here in South Florida, I have gotten 35
hours on the fine particle filter. I have also had to replace it
after 3 hours after sailing through several sarragasso patches near
the gulf stream.
Sounds like you did everything correctly when troubleshooting. You
probably just hit a patch of water with a lot of junk in it.
Joel F. Potter
Cruising Yacht Specialist
Amel's Sole Associate for the Americas