Tone,
As far as PH being affected I was remembering it can when its low in magnesium not high --SORRY !
I have had and do have bryopsis and have kept it under control by The same Methods you listed without elevated Magnesium which I have done but did not work for me.
The Magnesium Consentrate you mention was shown to me and if I recall it is nothing more than Off the shelf Magnesium Sulphate/Chloride--So it is Questionable What could be different about it !!!
I did say I thought 2300 was high and later you AGREED it was a bit.
As far as it being toxic at 2300 PPM You can't prove it will or won't as There is only test done with allot more mag to see if it killed things.
http://www.advancedaquarist.com/issues/oct2003/chem.htm
"Bingman12 pointed out in a previous article that at elevated concentrations (>8,000 ppm), magnesium has been used as an aid in shucking oysters, helping to force the oyster open,12-14 and also as an anesthetic for them.12 ****Consequently, magnesium does have potentially negative biological effects at significantly elevated concentrations."
Here is an where I get the idea of the balance being distorted---As I understand things Calcium will precipitate without magnesium and the saturation point or amount of Calcium is lowered.
(
http://www.fishchannel.com/saltwate...ums/aquarium-frontiers/calciums-little-sister)
Now if the Reverse is true And I can't see how it would not be-- The elevated magnesium levels would mess with the balance-Possably causing the Coarls to Change the levels they absorb calcium and carbonate and making it harder for them to do so(wouldn't they then need more elevated Calcium??). And at some point I would Imagine it eventually harms the process of coral growth and obviously if high enoughp if becomes anesthetic like.
So Thats what I know-- and What My Opinion's Are --And Why I think It's Not a good thing to go as High as 2300 PPM.
If you had said 1800 PPM I probably would not thought as Much about it Having myself Gone to around 1600 For 4 months !!!!!! ( I did not pay attention to growth at that time compared to now--wish I did)
Paul
P.S. Aquarium debacle
"Get a bigger protein skimmer "
My You have not seen his LARGE skimmer have you !! It's Massive--Now he may overfeed but his Skimmer is well Big Enoughp !!!