I ordered my Physan 20 from
Orchid Care - Orchid Culture - Practical Orchid Care Information
I used it for a problem similar to yours and I haven't seen much progress from my plant yet. I asked people about it, and a lot of people seemed to shy away from the stuff. Some said it was harsh and I needed to be careful how much and how often to use it, others said it isnt good to use when youre unsure whats wrong with your roots because your roots could have a fungal infection and Physan only treats bacterial infections.
If you want a first hand account about physan 20, well here it is: I suspected something wasn't right with my phal's roots. And before I read any threads on this forum, I searched the web and saw some places selling the physan. I bought it and read the instructions carefully. I did everything I was told to do. I took my plant out to repot, the soggy roots that I cut off I sprayed with the physan and then I made a bowl of it mixed with a gallon of water and sat the roots and crown in it for a few minutes. I carefully repotted it and now... every single one of my pretty flowers have fallen off and the spikes are slowly yellowing.
So, now I am left with just two yellowing bare spikes that were in beautiful bloom before using the phsyan.
Maybe it wasnt the physan 20 at all that caused this, but I can't think of anything else it could have been. All i know is, that "i" personally will not be using it anymore to treat a suspected problem unless my phal miraculously re-blooms.
I wish I would have learned about the peroxide, because I would have tried that instead.