Gregcoyote
Aquarium Advice Addict
We had this happen in an aquarium at the fish club's annual fish show. A member brought his actual tank in as many of the corals had grown onto the glass. I will say this tho, unless you have over the top filtration and a need to see a really foggy tank, I'd be glad they aren't spawning in your tank. WHAT A MESS!!! You'd be better off (IMO) having corals that send out buds or just divide better than mass spawning. Much neater and cleaner. Besides, how many of those eggs do you think will actually survive the filter?
I've seen it with big colonies of SPS corals, but my understanding is they are primarily the ones that spawn this way. Remarkably in sync with wild corals worldwide. Yes, it would be a mess and I doubt it is as effective as fragging to generate more coral in a closed system.