I will probably disagree with that. Just quarantine every single specimen. There are probably 2 school of thoughts. 1) let the fishes fight it out and they will be immune to it! 2) treat it completely in QT regardless of any symptoms and you will not deal with it eventually! What you are implying is point 1. Marine ich will always be in the system once being introduced. Fishes showing no symptoms of MI will not indicate that your system/fishes are free of MI. They are probably just resistant to MI. However, once stress (by adding new livestock or re scraping) is induced into the system, the fishes will probably lose its resistant to MI, hence an outbreak. All it take is just a small speck! By Performing A quarantine procedure, it will ensure that MI lifecycle will be totally breeched [emoji4] "it's just the nature of science and their lifecycle that you're battling". I have zebrasome tangs who used to be living in a tank full of MI which never showed any symptoms of MI while other fishes did continuously. I restarted the entire system, did a proper quarantine procedure and they are all good now. No matter how much my angels and the tangs hates one another and the amount of stress they created between themselves, they are currently still free of MI [emoji4] I've still yet to medicate my DT, however if there's a need I'll recapture all and dump all back to QTs. Sent from Singapore Reef Club mobile app