Alkalinity Up (Baking Soda) , Alkalinity Down (Sodium Bisulfate or MuriatIc Acid) or what is used to control your alklinity.

Note: When controlling Alkalinity always put the product in one spot in the deepest part of the spa.   If controlling pH you will broadcast the product. This is very important to remember and your Alkalinity will be much easier to controll 

Also when bringing your Alkalinity down you must add enough acid to do the trick.  Just adding small quantities will not work.  Spas take very little chemicals to adust the water so be causcious.  

Also When buying Muriatic Acid always get Hydrochloric and not sulfuric acid. Hydrochloric acid is clear or yellow and Sulfuric is reddish.  Sulfuric is not as strong and is sold in many grocery stores.  DO NOT USE IT!!!