Borax or Soda Ash

[mkenyon2]

I have 20 mule team borax and Arm & Hammer Super Washing Soda Detergent Booster at my grocery store.
The washing soda is cheaper per box, and according to the Pool Calculator, you don't need as much.

Which is better? What are the differences?

 

[JasonLion]

Washing sode, which is also called soda ash, raises PH quite a bit and TA a medium amount. Borax raises PH quite a bit and TA just a little. Often enough one or the other is preferred, but you can use either one in a pinch. When you are using trichlor, it is best to use soda ash to raise the PH, because trichlor lowers both PH and TA. But when you are using bleach, cal-hypo, lithium-hypo, or a SWG, it is normally best to use borax because using soda ash will tend to cause the TA to drift up over time.