If your top off water has a reading of 80, How high is your calcium in your tank? 400 to 450 is most people goal for calcium. Your calcium shouldn't be much higher than that, if it is you may need your calcium checked with a different test kit, to make sure the other one is reading correct. What type of corals do you have? How much Live Rock? I have a hell of a time keeping my calcium as high as 400-450, It gits absorbed pretty fast by a reef.