Pinklighter, I think water change is a good idea, but I would do 2 partial water changes rather than 1 50% one.
If fish seem ok try not to do the complete change. If you ever have to clean gravel rinse it in the tank water.
What is this staff that you used? Is there a warning on the packet that water may get cloudy till ph stabilises or something?
There must have been some chemical reaction in the tank taking place if you get this white fuzz.
What is your ph at the moment? And the other parameters?
If they are fine, do not worry too much even if the tank looks unsightly, it will get right in the end!