Well, I haven't used it on MJ before, but I have seen problems develop with soil pH (and eventually nute lockout) over long periods of regular application in landscaped gardens. But if you're making irregular applications (like less than once every two weeks), you won't build up enough in the soil, quick enough to make a difference.

Just read the directions, don't over-apply and you'll be just fine. Lookin' good, btw.