I may have rescued a betta that has Mycobacterium. He is currently in a clear plastic tote in 1 gallon water. I feel so bad for him, that I want to move him to a 5 gallon tank. While I researched about how to sanitize the items if or when he dies, I found various articles about povidone-iodine's effect on Microbacterium spp., in vitro to be 99% effective. So, my question is, can I use this to disinfectant the tank and stuffs in it?
Using povidone iodine in your tank is not a good idea it is harmful for most water living animals and it will stain most plastics.
If you want to do a total disinfection of your tank it is better to use hydrogen peroxide, as this breaks down to clean water.
Remember, after you have disinfected your tank you will need to cycle it for a month or more; cycling is done to build up bacteria that convert waste into plant food.
More information and details about cycling a tank could be found in this article.
Every time you disinfect or treat your tank with antibiotics you will have to cycle the tank again, the best way to avoid this is to medicate your fish in a separate tank.
The main reason for fish getting ill is a result of poor water quality, this is caused by overfeeding or not cycling the tank properly.
Before you go out to buy fish, take some time to read about the needs of the fish you want.