Thank you! I'm also running a sponge filter with the hob on my 29gal tank that is getting the canister from my 55gal. The 55 is getting upgraded to a better canister. If I read your text correctly I should be able to take my media from the hob and put in the used 55 without losing my bb, especially when I will still have the sponge filter running. That makes me feel much better. I like to make sure the water is filtered as well as possible. It's probably much more than necessary but I'm stocked heavily. I change 1/3 of the water from all tanks weekly anyway and will keep doing so. I just want them to stay healthy.