I have an fx5 here so I figure with my tank the same. If it's not super super crystal clear I can put that on there at first to help Polish the water but with. Little time and good filter socks I bet they will Polish the water super clean. When adding socks to an already setup tank it can take a while for them to get all the water clear as they have to go through all that volume and all the crud first. My next socks I might try some of the 100 and 50 micron soxks stuffed together. Time will tell and I will be posting what works best with my tank on my thread.