Emergency... mistake while dosing!!!

[reeferaddict]

Before you panic - don't do anything in a hurry!

If the animals are fine, then yes... do a water change and slowly lower your Alk... How quickly the levels come down on their own depends on what kind of animals you have that consume Ca+/Alk. Without supplementation, my tank will drop 50ppm Ca+ and 2 dKH Alk in 24 hours... if it were me, I would do a 10% water change daily, (to stress things as little as possible), until it comes down to a more reasonable level, 10 - 12 dKH is a good target, with anywhere between 400 and 450 ppm being good Calcium numbers. As you'll be doing water changes, Magnesium levels will be maintained that way unless you have some serious calcification going on. Then go buy a test kit to test and maintain Magnesium. Chronically LOW Calcium levels indicate a deficiency in Magnesium - (<850ppm)

The key to health is moreso an avoidance of sudden shifts in water quality rather than maintaining strict parameters.

Just my 2 bits... hope this helps!