Wow! I'm guessing its a seasonal or lunar-cycle thing, unless it's your after-shave cologne turning them on. Hope you succeed in raising some. I suspect you'll do better if you just try to keep a couple dozen in a 10 or 20 gal. If you have too many you'll never get enough food to them without polluting the tank. In nature they would scatter far and wide, not staying close together. They look much smaller than banggai cardinal fry. I'm sure the clownfish people here will chime in with advice (and food cultures).