Dasha

I got a second hand 33 gallon tank setup with Fluval 204 external canister filter.

My fist question is, how much of the ceramic media should be in the filter? I'd say I have about 10 pieces, the basket seemed half empty.

My second question is how ofter should I even open the filter and do anything with it, if it keeps running fine? Once a month to change the carbon?

Please help.

Isabella

Well, I don't have a Fluval canister filter, but I do have Rena Filstar's XP3 canister filter. What I do in my canister filter is I rinse filter media every month. My media don't get dirty and clogged up fast because my tank is large and very lightly stocked for now. Just check your filter regularly and see when it needs to be rinsed. If your tank is fully stocked, you should probably rinse it more often.

As for the ceramic medium, I have one full filter basket filled with it. The more bio-media, the better, because they provide a lot of surface are for the beneficial bacteria. I don't have activated carbon / charcoal / zeolite at all. I only have sponges and bio-media. The basket where the carbon is supposed to be is filled with more sponges. And the filter does a great job. But if you use the carbon, you should change it once a month. Carbon is effective for only 2 weeks or so (even less than that probably). If you keep it in your filter for too long, it may actually start leaching the toxins back to your tank - something you don't want.