I have spent hours and hours searching for a valid answer on this question after my discus got some parasitic infection (propably Velvet / Oodinum )from a damned plant Daniel . I ve found Very few if any valid info on this subject on the whole net.
The most reliable answer I got from Koi forums (they are BTW , always the cutting edge when it comes to fish science , mainly due to the very high prices involved in Koi keeping hobby ) were to dip the plants in a 25 ppm solution for more than 10 hours Maintaining that same dose by redosing if PP gets brown .
Why do we need the solution that strong for that long ? To hopfully kill the Nuke -resistant cysts of parasitic protozoas.
You can also use bleach/water solution in 1/19 ratio and dip the plants for 2 minutes for the same purpose instead of PP .