Its more about the length of time the tank has been up and running, and how much the copepods have multiplied in that ammount of time. I was told not to add one until atleast 6 months or a year has past, giving the copepods time to get their numbers up. Adding cheato works great, but they dont have issues living deep inside the rocks, only coming out at night. I would not suggest putting this fish in anything smaller then a 40 gallon. Also, adding a bottle of Trigger Pods, which is sold at most LFS's, is great to add to your tank to get the numbers of copepods up. Once you have high enough numbers then you are safe to add the fish. Also, they will learn to eat different forms of frozen foods. Most of the time they will "hunt" a floating peice of food, until it makes "live" enough movements for the fish to eat. Atleast thats what it looks like watching them feed on dead frozen foods. They would much rather a live, fleeing copepod to get after. Very cool fish.