If I had to take a guess, it would be that your pump problems stem from saltwater being somewhat abrasive. When used on saltwater, a submersible pump with a soft polypropylene pump head probably erodes 1/1000th of an inch at a time. Depending on the original manufacturing clearances, at some point the extra clearance results in the impeller being able to shift or tilt.
While I don't run SW
, I have had excellent luck with Danner Mag-Drive submersible pumps on FW
. Also, in non-aquarium applications on abrasive and corrosive fluids, I know that Little Giant makes non-submersible mag coupled pumps with fiberglass reinforced ryton pump heads which are much more resistant to abrasion and chemical attack. See http://www.littlegiant.com/LittleGia...lyPumpsWebView
. Using a non-submersible would require the installation of bulkhead fittings on the side of your trash can, but that shouldn't be a big deal to wind up with a single circ pump which will last for 3 years versus replacing two submersibles every 3 months !