So I noticed that my Sunsun 303B canister output was not putting out much water. I replaced the spray bar with a adjustable dual return nozzle w/flared ends from eBay a year ago. Spray bar restricts too much water flow but this dual return really lets the water flow out.
https://www.ebay.com/itm/LOC-LINE-1-...8AAOSwe-dfc4aB
Anywho, taking the Sunsun apart, verifying the impeller is just fine and putting back in action, still slow water flow... Hummm.
So I pull off the intake which has my coarse pre filter on the end and the water now shoots out the output! Well clogged intake pre filter. I just put on another and all is back to normal.