I am using Graeme Sait numbers that he likes to see on a soil test. I couldn’t find anyone else who talked about recommended soil test levels. I believe he suggests 2-4ppm. Not saying that is correct but when I’m trying to find information that seems to be lacking I’ll go with the best source I can find until I learn otherwise. Maybe I shouldn’t try to raise it up so fast? Not sure, not noticing any harmful effects at this point.