How to get rid of dandruff from thick curly hair?

i have thick, curly, dry hair. The best way to keep it healthy is to wash it twice a week. However, it does not work for me as the dandruff returns d very next day i shampoo my hair. If i wash them on a regular basis, it leaves my hair frizzy. I have tried anti-dandruff shampoos but to no avail. What can i do to get rid of the dandruff and keep my hair soft?