Usually, you can use anywhere from about 1-5 oz. I'd recommend using 2 or 3 and letting it sit until you like the flavor.
Also! When you're typing and the last few lines start to disappear, hit the plus sign (+) up next to the "Send" button, then hit "New Reply" at the top left. It won't actually start a new reply, but it will sort of refresh the page with all your typing still there, and you'll be able to see the lines!