I had about 150 pink zebra danio fry. After they were swimming for about 5 days, all of a sudden, all but about 10 of them died. I was feeding them "baby bites" (powdered food) made by Hikari. The parents were removed promptly after the eggs were laid and the fry were the only fish in the tank. I'm using a sponge filter. Any ideas on what went wrong?