Pull the fish out of the DT and treat them in another tank. Then, add your new corals and inverts to the DT and don't add anything else to that tank for 10-12 weeks. After 10-12 weeks is up, you can add your treated fish back in.
From now on, quarantine any additional purchases (rock, coral, inverts, fish) before adding them to the DT. This will give you the best chance of success.