120g sps tank with 9 fish. The main thing to watch out for with sulphur denitrators is your alk. Because you need low oxygen water to grow the anaerobic bacteria, the alk and ph drop a little. Most units come with aragonite media but personally I use only the sulphur media and keep my alk and ph levels up with Kalkwasser dosing.

They are a little like calcium reactors ,time wise, in that you have to watch your effluent drip rate and bleed off excess nitrogen every once in a while. But I've run into fewer problems with this type of filter vs other bacterial filters I've used.