Questions about carbon, cartridges, and filter media



After doing some research, I’ve realized many people advice against using filter cartridges at all; the reasons make sense to me (you’re getting rid of A LOT of beneficial bacteria every time you replace it). I just have a few questions:

  • If I were to create DIY filter media, do I need to include carbon? I’ve got a few plants and will be adding more. Does that change anything?
  • I have two HOBs for my 31g and each one has what seems to be two slots for fitler cartridges. That means I could have four total cartridges in my tank. Should I stick with filter cartridges and stagger when I replace each one to prevent the tank from re-cycling? Or should I put DIY filter media AND cartridges? Or should I skip the carbon altogether and just do some simple filter media?
What are your thoughts? Could you refer me to good articles of when and when not to use carbon?

Thanks guys :)


I don't think you need carbon at all unless you are trying to take meds out of the water. I recommend using sponges and/or media like Seachem matrix in the slots in your HOB filters.

Jerome O'Neil

Carbon, like all filter elements, perform some task. It's a tool. Do you need to clear your water of organic compounds like medications, tannin, and chlorine? Carbon is really good at that. If you don't, then it isn't going to do much for you and you could allocate that space for more biofiltration or something else.

I keep a basket of active carbon (and other filter materials like zeolite, etc...) and some filter bags around and run it when I need to. Otherwise, I just run a sponge for mechanical filtration, and the rest of the space goes to bioballs.


Regarding carbon:

It is very good at removing impurities from water such as medications. I find it most useful for removing tannins from water with new driftwood.

Other then that I never use it and never put it in a filter. It's a waste of space that could be used for media.

Regarding cartridges are replacing them:

If I ever have a filter with cartridges I throw them out before I start using the filter because for me they are a waste of money and do not make sense.

In your case with a filter running with cartridges allready in place you want to keep at least a part of them in there. Like cut out the carbon and keep the material bag part or fine sponge layers. Those are carrying your good bacteria. In the space created from disposing of carbon you can fill the filter with coarse sponge or even some ceramic porous rings.

Eventually you can then remove all the remnants of the cartridges once your new media has been cycled. Your filter media can then be rinsed out every month or so and you don't have to keep replacing it andd spending money.

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