Marineland HOT Magnum 250 problems

could be your motor going out :( or impellar.
 
That is weird. Try cleaning everything in the filter. Since you run your micron cart, your bio filter should be in your aquarium and thus a good cleaning shouldn't hurt much.

Clean the impeller are real well and then soak the impeller in a bleach solution for about 15 mins (your aquarium will be fine), then rinse it off real well. You should have gotten a pipe brush as well, use it to clean out the tubes.
 
Iv had the same problem with the strong pulse weak pulse, and mine wasnt more than a few months old. I threw that one out and got another and eventually it just looses prime. Seals would be my guess. Now it just sits with other unused filters.
 
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