12 days does it for ich and if there is brooklynella or amyloodinium(velvet) it should show up during that period. If it does then a longer period of qt with proper medication( formalin or copper ,respectively) can be done. It wouldn't hurt to move the fish to extended qt preferably in a larger tank, with say prazi pro treatment for those where flukes are common like wrasses can be since flukes sometimes take a few weeks to be noticeable unless you look very closely.
I've only taken in a few small fish since I stared this method one or two ata time ( a small juvenile sailfin, a small yellow tang and a pair of juvenille alardi clowns ) and use just 2 ten gallon tanks which are easy to empty ,dry ,refill and rotate. An ml of Prime ammonia detoxifier in each and light feeding works fine for ammonia control. Med free and less stressful for me and I think the fish as well.