Soft corals inhibit other coral growth?

Title says it all. Was reading a article about old tank syndrome which my tank suffered from. Still trying to make it better. Anyway part of the article it mentions how large established colonies of some soft corals release a toxin that inhibits other corals from growing. Even recommend fragging the large ones to cut back, since bigger colonies produce more chemicals. So my tank has alot of colt coral. Probably 5 to 7 years old. Stuff grows like a champ. Keep moving it down in the tank so it doesn't take over prime real a state. Is there a way to test for the chemical it puts out? Always run a bag of carbon in the sump and a UV sterilizer is plumbed into my return.

Any thoughts on this one? Figured I'd have to frag more of this out at some point but who likes giving away a coral that thrives? Hackshobby has a piece and it's doing great in his tank last heard.