How do I lower my Mg levels

[RPatsula]

Hi, I kind of screwed up my magnesium levels in my aquarium by dosing too much magnesium using my BRS 2 par solution. My magnesium level was approximately 1040 and I was raising it 100 ppm per day and inadvertently raised it to 1580 ppm. It has been at that level for approximately one week and I can't seem to get it to go down. My Ca is 400 ppm, Alk is 7, salinity is 1.023. I am doing a 45 gallon water change every second week. My total tank/sump water volume is approximately 280 gallons. I am thinking of changing my water change scheduled to every week until I get the magnesium levels to 1400 ppm.

So is the easiest way to reduce the magnesium levels, is to increase the water change frequency? I have stopped dosing in the meantime.
The direct result of the high magnesium levels so far is my torch coral has completely retracted, I think I may have killed him. Also my green bubble tip anemone has completely retracted as well and is hidden somewhere in my live rock.

Thank you
Rick