Two seems to be doing the trick. I vacuumed up some dirt that was going through before I loaded the Fiber Clear, and it seems to have stayed in the filter. Most have mentioned a need to do a lot of backwashing immediately after switching to Fiber Clear. I haven't had that issue, and my PSI is pretty low, and hasn't moved much over the last 2 days.

My guess is because I added clarifier and ran the filter 24 hours before cleaning the filter and switching to Fiber Clear.

After my next backwash, I'll see if I can get away with one package.