Does 18ml of 10% phosphoric acid sound like a lot of acid for a 5 gallon batch?
No, that's not much at all.
Cool..for this recipe i am about to brew 18ml bring the est mash ph to 5.38..would have preferred the mash ph to be closer to 5.2 but i want to use the least amount of acid i can and 5.38 should work out fine..thank you