I have had 9 different species of triggers in a 100 gallon tank. I reccommend to introduce them all at the same time while they are still small. If you do add one, take out all of the triggers, rearrange the aquascape, put the new one in for 1/2 an hour, put the others back, then turn off the lights if they start fighting. Live food sometimes distracts them. This has been successful for me, but I have lost more than one. Always add the undulate last. They are the most territorial. They are shy, but mean as hell. Picasos are the most persistant, but usually harmless eventually. If you add less aggresive species like pink tails or blue throats, give them at least an inch on the others. They can still snap at any time with little or no warning. Keep them well fed, and sit back and watch the comedy.