HI Shari800 and welcome to the forum.
Which fish is missing part of it's tail? I don't see anything that should be a problem withe the inhabitants except possibley the betta. Sometimes those work well in community tanks and sometimes they don't. My son had a betta in a tank for almost a year with no problems and then came home one day to find it had almost no tail or fins because something had attacked it that day.
If you can seperate the injured fish it would be best. You may not need to add any medication but melafix may help with the regrowth. The tail will probably grow back fine without any medication.
[snapback]911164[/snapback]