i wouldnt add anything to it yet. Make sure that you have completed the cycle. It can take several months to get through it.
Ammonia rises, then it will start going down as the nitrites rise. The nitrites will start to go down and the nitrates will start to go up.
When both ammonia and Nitrites are 0, do a water change to lower the nitrates
ammonia and nitrite are highly toxic to fish and inverts. that is why you want to make sure the cycle is done.