Replacing filter cartridge with media?

I have a cycled internal filter running on my 5.5 gal. However, the replacement cartridges are expensive and because there's a single cartridge in there I'm quite certain that replacing it will remove most of my BB and crash my cycle.

I have to do something before it clogs and eventually stops because it's already been cleaned in tank water a few times and it's slowing again. I'm waiting for a moddable HOB filter I've ordered but that won't be delivered for a couple of weeks.

I have some really good quality small ceramic media I can use that I can also move to the HOB filter when it arrives to cycle it faster. The issue is they won't fit in the current cartridge case unless I remove the cartridge which brings us back to square one...

I know I can run the HOB simultaneously for around a week when it arrives but that's two weeks from now plus another week for the cycling.

Is there anywhere I can put the media where they'll grow enough BB except inside the filter?

The current internal filter is a "waterfall style" cartridge

 

What about in the actual tank itself. They should be heavy enough to sink. Alternatively you can try to keep them in a net in the water or if you have some some cheesecloth or similar bag.

 

Yes they can sink but I'm not sure the flow on the bottom will be enough to grow sufficient BB. I could hang them from a net where the "waterfall" flows but that will kill my already slowing surface agitation.

The entire substrate is lava rock so I'm hoping there might be enough bb there to salvage the cycle in the worst case scenario

 

What about in the actual tank itself. They should be heavy enough to sink. Alternatively you can try to keep them in a net in the water or if you have some some cheesecloth or similar bag.

I second the cheesecloth

 

It's not the flow that grows the beneficial bacteria. It will grow on your substrate, decorations etc.

 

It's not the flow that grows the beneficial bacteria. It will grow on your substrate, decorations etc.

True but being oxidizing bacteria they thrive in oxygenated environments with continuous flow. The numbers anywhere else are only a fraction of the number found in the constantly flowing areas in the filter.

After some thought I am attempting to hack it in a different way: I'll be moving the cartridge outside the filter frame, in front of the intake. While the flow will be impacted, this should help keep a portion of the flow moving through the cartridge and keep enough BB alive. At the same time I will be putting the ceramic media inside the filter frame where water that is passing through from the cartridge outside will go though the media before cascading back into the tank right in front of the cartridge. Hopefully enough bacteria from the cartridge will stay alive while the new media is getting populated.

When the new HOB arrives I'll just move the ceramic media inside it and keep the cycle going.