[MyraVan]

If you have any carbon filter media in your filters, you remove that, but you don't remove the normal spongy stuff, since that's where your good bacteria live (the ones that convert ammonia -> nitrite and then nitrite -> nitrate). Carbon must be removed because it filters out the meds from your water, which is exactly what you don't want when treating fish! When they're all beter, you put the carbon in to remove the now un-needed meds. In fact, as far as I can see, that's the best use of carbon filter stuff: not to use it on a regular basis, but to use it to remove meds after your fish are well again.