I have always done 20% weekly water changes on my 120. The past few months I have cut back to 10% weekly water changes and dosing to keep up with alk and cal levels. Pretty new to dosing but I have always heard that alk and calc get consumed at a 1:1 ratio. In trying to maintain 9dkh alk and 440 ppm calc im dosing at a level that is closer to 5:1 im dosing for alkalinity every day and calcium maybe once a week. My first week of dosing I just tested the alkalinity and matched my calcium dose to what I was dosing for alkalinity (1:1) after a week of doing this I ended up with a tank that was 9dkh and 500 ppm. Only dosed alkalinity for the next 3.5 weeks until calcium level came down to 440. My mag level was 1200, just do not know why Im so off ratio and if I should be concerned.