I'm not sure what PFS stands for, but I'm sure you can let me know. When I do the grand switch-over I will take all my fish out and what gravel I can. Then I will put the Schultz's down and cover it with the gravel I have pulled out. I plan on doing this in one fell swoop, so the bacteria in the gravel will remain there. I think I'm getting close to switching everything. It should happen within the next couple of weeks. I'll try to keep some kind of photo journal, so anyone else in the same boat will be able to duplicate if I'm successful.