The first thing you want to do is figure out if them polyps have every strobilated in your care before. If they did, what conditions were they under. In my case, these polyps strobilated on their own three times last winter.
Now you start to experiment. If you have seen them strobilate before, try to replicate the conditions they were in. If not, try some of the common methods of strobilation induction. Common methods include,
1) Bringing the temperature down for two weeks and then bringing them temperature back up to simulate winter and spring.
2) Doing the reverse and simply bringing the temperature down and holding it until they strobilate.
3) Adding Lugol's Iodine to the polyp water. For this method, turn the flow off if there is some, and add 3-5 drops. Iodine levels increase in spring, and the polyps recognize this.
4) Your own experimentation. There are other methods of strobilation induction. Some include shaking the polyps for several days (on a shaker table, no need to wear out your hands), exposing them to light for a time and then darkness, or reverse (particularly hydroids).
In my case, I tried all but the light period method. I started out not having a chiller, so I couldn't drop the temperature. I was afraid I would kill my polyps if I brought the temperature up anymore. So I decided to try iodine. I did this several times in varying amounts, and it never seemed to work. I took some polyps and set them in a small bottle. I put this bottle on top of an air pump so it would shake the polyps constantly. This had no success either. Finally I got a chiller, so I decided to lower the temperature and bring it back up. That method is one that works on almost all Moon Jellyfish. I lowered the water temp to 60 for a week and then shut off the chiller. No strobila. I gave the polyps some time to rest and then decided I would chill them at 55 for two weeks. So my chiller isn't very powerful, and it is about 80 outside here, so my chiller fluctuates between 55 and 60. Right at two weeks I began to notice the polyps were elongating. So I left the chiller on. Within a week, they began to form full strobila. And then the onslaught of ephyra began. I have never seen so many ephyra in my life! I must have 1000-2000 right now! My polyps really paid me back for holding off all spring and summer. Now I need to build more tanks for all the ephyra.
So to wrap up, I believe the chilling induces strobilation in this strain of Moon Jellyfish. I can't be certain until I try again, though.