This is similar to my thought process as well, thank you for the inputTo op, I'm doing 45 days and to most that is more than acceptable. Whenever you add something to dt there is always risk of something. Unless we want to hold our fish friends in qt their whole life there will be that small chance of parasites returning no matter the length of qt. You could keep them in qt for a year then have the dt contaminated by a net or something similar. I am getting my fish healthy and fat in qt with a solid varied diet while allowing dt to be fallow for 45 days. I will not be 100% sure the display is free of all parasites but I do believe my fish will continue to stay healthy and not become infested again as long as I take care of them the way they deserve.