Didnt have any carbon on it yet. Wanted to "dry" run it for a couple days. Added some PRIME to the tank to cover any nasties. Been running for 3 days now & everything seems to be peachy. Automatic drain I set up in the sump seems to be perfectly keeping the sump level right where I wanted it & the drip is a nice constant refill. Water is crystal clear & fish seem super happy. All is good so far.