It is always stressed in this hobby to quarantine new fish before introducing them into your aquarium. The idea is to prevent any and all diseases and parasites from infecting your current stock of fish, while also helping new additions adapt better to captivity with specialized care. While the quarantine process is vital for long term fish health, it is also important to quarantine new corals. All corals are subject to parasites and disease, and one you introduce an infected coral into your aquarium, the health of all the corals is immediately in jeopardy. For a coral QT, you want to identify any possible problems and fix them before the coral makes it to your tank. This means treating parasites with medicine and even making multiple attempts to disrupt their life cycles. Only after a coral has been verified pest-free for several weeks should they be introduced into the main display.