What Is The Folic Acid Dosage To Be Taken For Ankylosing Spondylitis?

Hello Sir, I am suffering from Ankylosing Spondylatis and i am taking Etoricoxib 90 gm every alternate day once. taking salfasazine 1gm daily twice. These two tablets i am taking currently since couple of months. I was suggested to me to take folic acid 5 mg but I forgot the dose of it. Could you please let me know the dose of folic acid that i need to take and suggest if the medicine that i am taking is proper or not?