Help! Big spot on new Phal.

[B3finga]

Hi, this is my first post here but surely won't be my last. I just bought this Phal. yesterday and the potting medium was all moss and waterlogged so I thought I'd repot it immediately. I got rid of all the moss, cut away a few rotten roots and sprayed them with peroxide. I noticed that some of the roots, while healthy looking and fleshy, had a pink tint to them. That was a new one for me. I repotted it in a fir bark mix and gave it some water and put it on a shelf with the rest of my plants.

This morning, I woke up to find this big spot on one of the leaves. I've done my research and think it might be a bacterial infection. What should I do?