Just a word of caution.
If your MG is already at 1600. getting kent magnesium will only raise it even more.
also raising magnesium high is also not a sure fire way to get rid of bryopsis, especially if there is plenty of nutrients available to the algae, especially if its in the rocks its growing on
No doubt there is something about kent magnesium that might get the job done, the worry i have is his Mg levels are already sitting at 1600ppm.
So the question now is to raise it further to get a decent concentration of kent product to be effective and if so how far is enough?
Or does he do water changes to lower the mg and then re-raise the mg levels. and if this route is followed how much strain will it put on his system?