Acid malt advice

I'm toying with the idea of using acid malt to add a slight tartness to a 6gallon batch. What amount of acid malt will give a mild tartness? I'm not looking for mouth-puckering tartness, just a nice touch. Thanks!

I have used it a few times, notably in hefeweizen and Witte. Usually kept it down to 2 - 4 oz. it did seem to come through with a slight twang. I am too afraid to use much more. Some Hefe/Witte yeasts can also give off that twang so I can't really be sure if it was the yeast, the malt, or a combination.
I had done some research when using it a few years ago. I can't remember anyone looking to add anymore than a few oz. unless a sour beer was intended