Can I add coral to a tank

[gregzz4]

To add to what Brad stated, it's OK to add things to a tank that is sitting fallow, but what you add may bring with it 'things', so it's best to dip or better yet quarantine stuff before you add it to your tank
Just don't ever add ANY corals to your tank without first dipping and thoroughly inspecting

As for the corals you have in QT that were in the tank that had velvet; let them sit for the 3 months before they go back into your DT

What are you doing with the 1 fish you have left ?