400W is a lot of light and if you're having bleaching problems that would certainly be my first guess too. Try moving your lights up further, moving some coral down more, perhaps cut back on your photoperiod and remember to slowly acclimate coral by starting it off low in the tank.
You're magnesium is also a little on the low side and your phosphate and nitrate are a little high. Detectable nitrite is also really toxic. I'm assuming you mean Alkalinity 10.0 dkh?
A picture is also worth a thousand words. Do you have one of your tank/setup that you could show us?
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