Since I have recently gone through this process and since I feel that there could be more threads about this subject, tonight I wanted to add my .02 on how to customize HOB
cartridge based filters such as, but not limited to: the Tetra EX series, API Superclean, TopFin power filters, Aqueon quiet flow and many, many other filters that force you to buy cartridges.
So a quick background on my aquarium: my tank is a 20gal Tetra brand starter kit that included a EX20 filter from them, a full hood, samples of their products, and the store we bought it also threw in about $30 worth of plastic plants. For the initial setup, we just began using their filter and of course put in the cartridge it came with. My tank was set up in early January. Thanks to the awesome advice I got on here, I did a fishless cycle and the tank cycled fine. Just before I added my fish, I noticed that the EX20 seemed to have issues keeping the water crystal clear, which I felt was odd considering there weren't even fish in the tank yet. I knew of how good the Fluval/Hagen HOB
filters were and decided to purchase an AquaClear 50 (which is still running like a champ). This was now around early February. I didn't want to start the AC
50 and have nothing to help seed the new filter so I decided to run the EX20 along with my new AC
50. By this point I already know a good deal about custom media for AquaClear's so I never used the carbon pouch it comes with, just various sized sponges from Drs Foster and Smith. These are the sponges I use from them:
Aquarium Filter Media: Drs Foster and Smith Mechanical filter Media
I would highly recommend their fine, super fine, coarse and micron polishing pads.
Anyways, several weeks ago I looked at my crappy EX20 cartridge and thought to myself there has got to be a way to make this thing customizable. And then it hit me: what if I used those sponges from Drs Foster and Smith and cut them to size to fit the frame where you usually put the cartridge? YES!!
It worked perfectly!! Now granted the sponges are a bit wider then the cartridge frame so it pops out a little but that doesn't deter the water from passing through as if the Tetra brand cartridge was in place.
So as of right now I have one side of the cartridge frame with a super fine sponge in it, and behind that I have a piece of the Acurel brand debris catching pad (another excellent filter media I highly recommend). I then decided to take my customization one step further by increasing the bio media for my tank. I bought a bag of bio media for an AC
50 and took out the crappy plastic "bio scrubber" that the EX20 came with. I figured I wasn't losing too much bacteria as the bio scrubber had virtually nothing on it. I stuffed the bio media where the bio scrubber was and it was a bit of a tight fit but it fits and I feel that once that bacteria colony fully develops, my tank will be "supercharged" with beneficial bacteria
These are pictures of what my custom media setup in the EX20 looks like:
This is the Acurel debris catching pad, facing the front of the filter
This is the super fine sponge in the back (where the water first comes into the filter
And here's a shot of the entire cartridge holder with both sponges
Hopefully this thread can help people. This forum has helped me so much I thought it'd be nice to share my experience with customizing filter media and to let folks know there is a MUCH better alternative out there than being forced to buy those overpriced and ineffective HOB