Hmmmm well Idk Teugelsi from what I have seen get bigger than Ornates and Weeksii so I wouldn't recommend keeping a teugelsi in that foot print. I'd stick with any Upper jaws besides teugelsi, ornates, and weeksii. However weeksii take forever to grow so you could house the weeksii for a long amount of time before you would have to consider rehoming or retanking it. I would say with the polys you have now you could add about 3-5 more polys to stay on the comfortable side. Once you go over that amount if you over filter you could still be good, but it may start to get crowded. (that is not including ropefish since ropefish are we slender and flexible they can easily maneuver in the 18" footprint you can fit about 5-6 ropes along with about 6-8 polys)