Best way to cure a planted tank?

I have a 6.6 gallon Petco bookshelf tank stocked with 1 male betta (Gwendle), 2 otto catfish, and about 10 ghost shrimp. I recently discovered Gwendle has coloumnaris, (he got it from some neon tetras I added as tankmates before ultimately removing them due to improper stocking) and these are my questions.

1. What is the best medication for treating coloumnaris?

2. Where can I get said medicine and is it sold at big chain stores? (i.e. petco, petsmart, etc)

3. I have a planted tank and want to keep it that way; is there a medicine that won't require a separate tank for medicating or won't harm my plants?

4. Will my ottos and ghost shrimp need to be treated as well?

The otto catfish will be moved eventually to my 20 gallon, but right now it is housing a goldfish I'm waiting for my cousin to take back, so please no lectures, I don't want to hear it. I just want to heal my fish so they can go back to their lives and I to mine.