I have above water filter that uses ceramic media on top of a poly filter. How frequently should I change the poly filter? It's currently pretty dirty after two months but I guess it's supposed to be (it's a filter after all).
I usually change the filter cartridges on my FW tanks at least once a month. It depends on the size of the filter and the bioload in the tank. As Allivymar stated, when the water flow slows through the filter, it's definitely time to change it.
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