As soon as we open our pool, I am planning on using the acid to remove the stains on our liner. How much of it do I need for my 27' AG (48" deep) pool?

Also, If I remember right, I also need to use some Metal Out afterwards. Am I correct?

This is the Absorbic Acid (Vitamin C) I will be getting...http://www.chemistrystore.com/Ascorbic_Acid.htm