rabbut
I don't bite, all that often...
Without knowing what the first cartridge is, it is difficult to know if needs replacing. The sponge and ball media don't ever need replacing. Simply do as you do ATMI would replace that cartridge with some more sponge, to create a low maintanance and cheap to run filter system, as none of the media would need replacing
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HTH
Rabbut
its a cartridge with a tiny bit of sponge in it, and then it has some carbon in it. Rather useless tbh.
Would definately replace with a sponge or similar media then
Rabbut