Hi everyone, Please dont beat me up to bad with what I have to say. It worked for me for 3 years until I took the set up down. With a tank that size of 155 gal U can add more than 3. When I lived in Sandiego, Ca I had a 55 gal fish only. What was in it you ask 1 kole tang, I hippo tang, 1 yellow tang 1 koran angel. Never had a problem as I introduced them into the tank I moved rocks around to limit the aggresion from the current residents. I know some of you may say its crowded or it wont work, it did for me until I took it down and moved to New Jersey. Just my 2 cents:invisible