When I notice a difference in flow rate I will brush the intakes, as well as remove & clean the impeller & brush the housing.
I have never set a schedule, I just do it when needed.
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The HOB carts get changed sometimes.. again no schedule.. I remove the first line carts & move the second lines to the first & put 2 new ones in the second line to build them up, thus keeping the bio balance.
its all very scientific. if they are clogged but the water is good, then I rinse.
I know this doesn't help, but each of my tanks is different.
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rule of thumb, ALWAYS read the directions so you know what not to do
i havent cleaned my fluval in a long time water checks out perfect all the time so i havent found the need to clean it my wet dry pre filter pads i change once a month or when they are really dirty
The manual for my filters say to change the cartridges when they overflow or monthly. Will it hurt if I let them overflow for a couple of weeks even if it has been a month?