I used a plastic Critter cage ai picked up from Walmart for about 8 bucks I used a hot soldering iron to melt some poles round the sides and the top and the bottom two for more flow through it. I added a 4 inch purple tang to my 120 which already had a 5-inch yellow tang. I kept the purple in there for about four or five days it should have been longer. As it turns out the purple is far more active and aggressive than the yellow and has pretty much taken over the tank relegating yellow to a back corner. I'm probably going to trap the purple at some point and move him on. Good luck