I've had similar issues with canisters. They simply just decline in function too fast for their price. I have over the backs that are over 20 years old that still push water at what appears to be the same insane volume. Mean while my relatively young marine land seems to struggle to push water when in pristine order.
I'd just give up on canisters. The ADA filters are not for normal people but people with money to burn. I'd say if quality of filtration and functionality is your concern its time to sump! You can build a very efficient easily serviced superior sump alternative for not much money with a simple visit to target and homedepot.
Imo exp and others ive only heard bad things about marineland canisters/products. I wouldnt let them ruin ur opinion of good quality canisters.