What is your plan after you clear velvet from your DT? Are you going to QT (treat or just watch) every fish you buy? Corals can also bring things you do not want into your tank.
Check out these two links.
https://www.reef2reef.com/threads/coral-invert-quarantine-time-frames.334584/
https://www.reef2reef.com/threads/how-to-quarantine.189815/
After learning the hard way, I am going to be QTing my fish, but not my corals / inverts.
For my inverts, I plan on ordering them online from a vendor that doesn't have fish in their systems.
For my corals, unfortunately I am going to be rolling the dice (I will be dipping whatever I can, and hopefully shooting any bad things off with a baster).