I spoke with Triton labs. They said that there info is based on when people used to blindly dose chromium in there tanks (funny how fads come and go in this hobby lol) with resulting excessive levels. They said it can effect some staghorn corals! That was it !You'd have to ask them how they set their recommendation bars.
I do agree that keeping levels in line with natural sea water is a great goal but in a closed system it is a real challenge.