I am just wondering if the carbon filter will remove the remainder of the Ich-X medication from my tank after I put it back in, in two days? Or should I do an 8 gallon water change? I have a 16 gallon tank...
Yes, it is likely to remove it and yes, you should do a water change. Directions usually tell you to remove carbon before treatment and that carbon will/won't remove it.
Regardless of whether it does or not, you should always do a partial water change after treating with a medication.
Agreed, may as well replace all the media while at it. I like to replace my filter media every 6 weeks my Discus do well with that; my water pump/filter are Penn Plax Cascade 1000 for my 55 gallon tanks.