Water changes would be best then to keep it balanced with the Ca
and possibley correct any difficiencies in the Mg
levels. I would also allow your Ca
levels to drop down with it. Try not to allow the Ca
to get above 450ish ppm
. If too high you could risk precipitation as well as possible tissue seperation from the animals scleractinia.
@ 450ppm Ca
the balanced alk
would be about 12ish DKH
or 4.25-4.5 mEq/l. In your case about 215-225ppm.
Also be aware that when testing these levels, they should be done several hours after any chem additions or water changes to allow for proper settling and the mixtures to balance chemically. If testing too soon afterward, you will get false/skewed readings.