ummmmm i dunno how many mantis you have gone through feeding them like that but from what I've heard it is feed them a piece of food the size of their carapace every couple of days maybe every other day, i feed monte my mantis shrimp with only live things, so i keep her tank stocked with fish and snails and from there she finds them, sometimes i give here a fresh shrimp snack, usually i spend close to $30 a week on live food but that can last a couple weeks sometimes, the other day i bought a pound of fresh shrimp for $8 and thats good enough for about 40-50 feedings