Post-whitespot Plans

Sorry Diz, just realised I've not posted yet 

You need to wait until you are sure the whitespot has gone. I would wait 2 weeks to be on the safe side although any re-infection would be quicker than that.

New fish should be kept in QT for a minimum of 2 weeks. Some people say 4 weeks. And if you ever have discus, it's longer than that for them.

Basically you need to wait until you are sure there are no stage 2 whitespot (the cyst on the bottom of the tank where they multiply) lying there ready to release the 'baby' whitespot bugs. In theory, some could have been sucked into the filter. Two weeks is more than enough time for the slowest cyst to open and the spots on the fish grow big enough to see.

With the new fish in the QT just watch them. They've been through enough without putting med in the tank as well. If there is no sign of any spots (or anyhting else) in 2 weeks, they should be OK to go in your tank. I once quarantined new fish for 8 days and the day after I put them in the main tank they had spots on them