At the university, I mix up a gallon and the students dunk their film in it after washing. It stays on the counter (w/lid) for a few days until it just starts to get cloudy. We have done this since at least 1978 when I took my first class there...and probably the 20 years before that. I recommend that the students see-saw the film through it, but some dunk the reel w/film into the tank.
No problems -- unless someone mixes it up a little strong.