Guthix balance potions are modified restore potions. To make Guthix balance potions, the player has to have partially completed the In Aid of the Myreque quest and must have at least 22 Herblore. Restore potions are made from harralander and red spiders' eggs. You can use a restore potion of any dose. To make Guthix balance potions, add garlic to make Guthix balance (unf) potion and then add silver dust (made by using a silver bar in the Grinder at the Ectofuntus). The potion cannot be made until after you have "killed" Gadderanks, and talked to him, at which point he will reveal how to create the potion.
Guthix balance potions are used against frozen Vampyre Juvinates. After freezing the Juvinates with the rod of ivandis the potion has three outcomes: The vampyre will be destroyed, the vampyre will become angry (and vulnerable to all attacks) or they will be returned to human form.