There is an
online owners manual at this site.
Scroll down until you see the model number of your filter (it will be the second one), then click on manual.
When you say charcoal, I'm assuming that you are talking about the carbon?
I have a fluval, not the same model, however my owners manual never indicated when to change out the carbon, etc.
I change the carbon once every one to two months and I never change the bio media.
The instructions and usage for carbon and other filter media replacements are always listed and indicated in the directions on the box in which they are packaged in or on the package insert..
Linear Mode
