Why are you running the Floss, I find that it polishes the water but can also trap detritus.It's OK to use it but should be changed often, I know you're gonna want to introduce Corals very soon, wink, wink, Nothing wrong with doing a water change. It's just that you'll want to bump up your S.G. once you put Coral in there and you don't have a lot of time before the fest.
If I were you, I might do 20 percent to get the Nitrite down and keep testing, see how it is by Friday/