Carbon is useful for removing toxins from water (metals, medication, etc). Most fishkeepers do not constantly run carbon, because there's no real reason for it on a daily basis. You'd be better off using some type of biomedia in its place. If for some reason you need to add carbon, just keep your biomedia in a little bag, so that you can pull it out, throw it in the tank for the time being, and put your carbon in. HOB filters, especially the bio-wheel, just aren't ideal for tanks which need heavy filtration. However, if it's what you've got, and you can' tafford anything else right now, filling it with as much biomedia as possible is the best you can do. As for your ammonia problems, this is going to happen, becuase your tank is cycling all over again. You'll see nitrite rise, and then go away, and until you've got 0 ammonia and 0 nitrite, you're not done cycling. Obviously, since you have fish, this is going to have to be a slower process, because you can't let ammonia spike so high that it kills them. Do your constant water changes like you were doing for the HITH guy, this will keep ammonia lower. The only option you have to really nip this thing in the bud quickly is a product called Dr. Tim's One-and-Only. It is a beneficial bacteria that actually works. It costs, but it works, as opposed to other Bb-in-a-bottle which may be a little cheaper, but does pretty much nothing. They sell it at Drs. Foster and Smith. I've never seen it in an LFS. It is on sale right now, though. This is what I used to cycle my pond. It definitely works. So, what it's going to do is put those bacteria in your tank, without having ot wait fo them to grow, which is the cycling process. Please ask if you have any more questions.