Yes they are expensive. For filters I have 2 eheim 2262, 3 eheim 2028 and a sunsun 4 stage. Cost of filter material are around $330.
BUT...in an enclosed system like a canister, pot scrubbers have far less bio capacity than these materials(eheim substract pro), and clogs up way too fast for my liking. If it saves me 10 cleanings a year, the extra expense are well worth it.
I can see pot scrubbers can replace bio balls in wet dry applications where separate mechanical filtration state can eliminate much of the big particles, and easy to access. In a canister, they do not hold any advantage to traditional biofiltration material(of course, one should not use bio balls in a canister anyway.)
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