Alright, Koko wanted me to repost this here in a new topic.
Many people that are new to fish keeping, fall for the replaceable filter cartridges that are sold by the companies that make the filters.
By doing that, you will toss out the majority of your beneficial bacteria every time you replace a cartridge, and so continuously experience cycle bumps, which can lead to health problems for your fish; not to mention the amount of $$ you waste when buying the filter cartridges.
First off: Carbon is not necessary. Only if you need to remove medications from the water, or to remove odor (which usually shouldn't happen in a fish tank, except for a light smell similar to wet soil).
Carbon collects impurities, but if the carbon is "full", these impurities will leech back into the water and can cause health issues.
This is how I set up all my HOB filters:
Get a pack of Marineland Rite Size Undergravel Filter Floss, which costs about $ 6. http://img.photobuck...-filter-pad.jpg (it contains one big, folded up sheet of floss)
Get as many boxes of Fluval Bio Max Ceramic Rings as you can fit in the filter. They are around $ 13 each.
Remove your current media and keep it in a container of tank water.
Cut a piece of filter floss out of the Marineland Rite Size to fit into each of the filters. Only one layer each, and put it in the filter in a way that the water HAS to go through the filter floss first.
Fill the bio rings (rinsed under water first to remove dust) in the available space, as many as you can.
This here is what the end product looks like
In order to keep as many beneficial bacteria as possible, you should additionally add your current filter floss. If you can, remove the carbon. The plastic holders can go in the trash also.
Do NOT rinse your floss in tap water, the chlorine will kill the bacteria.
Then just have your old floss between the new floss and the ceramic rings. The bacteria will start multiplying and spreading out onto your new media.
The floss is what will collect most of the gunk. Rinse/swish/squeeze it in used tank water if they get gunky, and re use. If they are beyond saving, you can replace the floss with a new piece.
The ceramic rings might need occasional gentle swishing in tank water to remove gunk and will last for a long time.