To do hypo, you must have a refractometer, and it must be precisely calibrated. Even slightly off, and hypo will not work. The only way you can do hypo safely with certainty is in a separate tank and leave your display fishless for at least 8 weeks. If you do it in the display, there is going to be the ammonia problem mentioned in the thread on cupramine in the display posted above you are going to have to deal with. Read about the fauna die off and how to deal with it in the cupramine thread because the exact same problem will exist if you hypo your display. To hypo the display, you are going to need some ammonia binder, live bacteria, and lots of mixed water precisely to hypo level ready for many frequent water changes. At the same time, you are going to have to constantly test for ammonia and remove as much organic matter that you can before or as it dies. This is all explained in the thread and particularlly one of the threads referenced therein. Even then, there is a real chance that you may not be able to manage the ammonia and kill all your fish if you hypo the display. You are going to have to be around the tank 24/7 and constantly managing ammonia for about up to 1 week to succeed at hypoing the display.