Need Help Upgrading Filter Media Without Crashing Tank

So my 20 gallon long tank currently has 22 harlequin rasboras with a Marineland Penguin 100 and a sponge filter designed for 10 gallon tanks.

Now the penguin filter was cycled with this filter bag wrapped over the intake, and I assume a lot of bacteria is now growing on there. It's pretty ugly though, so I want to replace it with this sponge I ordered. The sponge was designed to go over the end of one of these and will look way better.




Second, I have the stock filter media/charcoal combo or whatever it is they put in the back, with a bag of Purigen in the front. I'd like to pull out that filter media and put in a bag of ceramic media that I got for my Aquaclear 70.





So how on earth do I switch these out without screwing up my cycle?

 

Put as much of the ceramic media in the filter you can with the old media. The ceramic media will colonize with bacteria over time and then you can remove the old media. If the filter bag will fit over the sponge that you want to add, then add the sponge and put the bag around it. The sponge will also colonize over time.

 

BB grows on every surface in the tank. The filter bag over the intake doesn't have as much as you would think so it's not a big deal. You can swap it out with no issues.

Put the BioMax (ceramic media) under the Purigen. You can cut the filter to get the charcoal out of the pad and just use it as mechanical filtration. There's no good reason to have charcoal filtration in a tank unless you're trying to get meds out of the water. Same with Purigen but it probably has some BB.

The rest of the tank should have BB on its surfaces so your tank shouldn't crash. You might have a minI cycle but just feed your fish less for the next week and you'll be fine.

 

Cool thanks guys. I use the charcoal just because it was part of the filter that came with it, and I use Purigen because it sucks all the tannin out of my water and keeps it away. We don't like the dark color.

 

I ended up removing the whole piece the charcoal is attached to. Supposedly the biowheel on these things is supposed to hold all my bacteria anyway. I also removed the mesh off the intake and put the sponge. The HOB part now has the purigen on top and the biomax under it.

I'm thinking (hoping) between the sponge intake and the sponge filter on the other side, I'll have plenty of mechanical filtration on this tank.

 

So I checked today, around 24 hours later, and ammonia and nitrite are still both 0, so I guess we were completely successful. Thanks again for the help!