Well, I'm no poo, but I haven't had any dandruff issues until I had used too much baking soda and had THAT flaking...

I've heard that if you dilute 50/50 water and vinegar and pour/massage that on your scalp, this can help a lot with dandruff. For me personally, vinegar makes my hair greasy, so I use tea rinses instead... lavender is suppossed to be antiseptic for the scalp. I add some dried lavender to hot water and let it steep. Then I strain the cool liquid and pour that on my scalp and massage.

I think even just using rinses should be enough for you even though you are working out. After all, sweat is just water and salt. Try it and see.