~ Co-precipitation with an EXCESS of Calcium/alkalinity in solution.
~ Coralline algal formation
~ Tridacnid clam
~ other Molluscs
~ SPS, and LPS coral
~ Soft coral
You'll find NSW, and supposedly your Reef aquaria
Magnesium : Calcium RATIO in order of just over 3:1
Looking at Mg : Ca as 1300ppm : 400ppm , that's just peachy!!!
Your Magnesium presence is NOT TOO HIGH...far from it, in fact after Sodium/Chloride, Magnesium is 3rd most abundant ion in NSW.
PRACTICAL MAXIMA, are almost an impossibility, seeing magnesium is already quite high in concentration in normal seawater, so to significantly elevate it requires conditions that would rarely be encountered in oceans or even lagoons.
[source: Magnesium in Reef Aquaria ]
by Randy Holmes-Farley http://www.advancedaquarist.com/issues/oct2003/chem.htm
Based on facts from source cited below... that Mg >8000ppm levels are used to anaesthetise shellfish, and to assist in SHUCKING/opening Oysters (for the table)
It reaches a TOXIC LEVEL, when toxic effects are observed....and in your case it would be around 6 TIMES MORE....
"Oh Shucks! It's OYSTER!!!" ??!!
[FONT=Times New Roman, Times, serif][Magnesium — Part II][/FONT]
[FONT=Times New Roman, Times, serif]by Craig Bingman Aquarium Frontiers April 1999
Simplistically....KEEP an eye on Ca:Mg Ratio, and if you maintain min Ca 350 mg/L, you should aim for min Mg 1050-1100 mg/L.
Again, I can't stress the importance accuracy plays(relatively speaking), in Ca vs Alk vs Mg test results.
It's no use if any 2 of them are obtained with BROAD-RANGE kits, while 3rd parameter is NARROW-RANGE....becomes untidy when you try to determine if all is well and no cause for concern...