It seems odd to create a breeding thread/journal for something that you have spent nearly a year trying to get rid of, but I figure someone out there might want to know...
I don't know how I got these things. My best guess is that they came in on some cerith snails I ordered, probably a polyp or two. Maybe they came from somewhere else though...I feel like I have seen the polyps in other tanks, but they don't get beyond that stage and turn into full blown jellies. Perhaps other things eat them in the other tanks. I do know at one point I saw the polyps in my paly/zoa/polyp tank but they disappeared....I figured the peppermint shrimp ate them. I can't remember if that was before they became overabundant in the biocube or after.
For the longest time I thought they were just hydroids and I would siphon them out and scrape them off. Even when I realized that they would become jellyfish, I would siphon them out.
Here are some polyp pics:
This pic shows a brown adult and a blue adult. I've also seen green ones in that tank. The blue are by far the prettiest.
And here is a backlit shot of it (in a clear measuring cup)
Here is a brown one on the glass, next to a columbellid snail:
I do absolutely nothing special for them. I feed the fish in the tank and they must get enough of what they need from that. I have been working on IDing them, but Cassiopea is as far as I got.