I am fairly new to the betta community. I have had Mr. fish for over a year and he is doing really well. I have recently purchased 3 moreand am trying to do better by them. I purchased a new tank today and will be setting it up tomorrow (dividing and decorating it) and letting it cycle for a few days before I put the fish in it. Al, my biggest is very aggressive and I believe he will stay in the 2.5 gallon tank and I may purchase another guy to go in the divided 20 gallon long that i will be setting up. Al, the big guy in my profile pic, seams to have split his tail pretty good the other day and now it is starting to form brown streaks in it. I understand it is most likely fin rot. I am trying to treat it with clean water and a little bit of extra stress coat, I have taken all decor out of his tank but some soft plants for him to rest on. What else can I do to help him?
Also, before i set up the big divided tank, what additives should I put in the water, besides stress coat? I will be picking up a test kit in the morning so I can start testing the water like I should have been.