My partner has pretty bad dandruff on his head and beard,
Try the following:
Get a squeezable bottle like mustard/ketchup bottle or empty shampoo bottle.
The formula is 3/4 ACV +1/4 distilled water (non chlorinated water) + 1/2 teaspoon (or more) baking soda + 1/4 teaspoon borax.
How to make it: fill 1/3rd bottle with ACV, add the baking soda a bit at a time, wait for the foam to subside add more,... add the borax, mix thoroughly, fill to 3/4 bottle with ACV, mix again, top it with distilled water, mix.
Use it after each shower as hair conditioner. Some say rinse after 10mnts. I don't bother.
Another suggestion: stop using shampoo & conditioner. I use olive oil soap, castille soap (or any oil soap) instead of the chemical smorgasbord they call shampoo/conditioner, it's good for your carpet not for your hair.
My hair used to be like a salt shaker full of dandruff with itchy scalp. Although the problem has been solved long ago, I still use it, my wife too, and will always do, it makes your hair silky,
