I read somewhere that they make separate vitamin tablets or something for fish outside of the ones in their food. This is supposed to be good for building up their immune system, especially if it is currently lacking.
Is that true? Should I find some of these vitamins, or just stick with good quality food and the occasional does of aquarium salt when my fish isn't looking so good?
Stick with a good quality pellet, but it's also good to vary diet a bit. My guy got frozen bloodworms once a week as well as fasted one day a week. A good quality pellet and a good water change schedule will help your betta. :)