im not familiar with kent Ca and if theres any other additives in there, but ive never heard of a max daily dose of calcium. Its one of those elements where you need to dose based on how much your system uses.
I know some additives i have show beginner, intermediate, and expert usage instructions with the beginner instructions specifying a suggested amount of product to add based solely on tank size. These instructions are usually assuming the person will not test the water to see how much of what ever they are adding is actually in the water.
The more advanced instructions usually have a starting range then basically just say test your water and adjust as needed. If thats the case for this kent Ca, then i wouldnt suggest doubling it, but maybe adding an extra 1-2 ml per day, test after a week and see where you stand. If the Ca is the same as a week prior, or decreasing, then i would usually increase the dosage again. If the Ca is increasing i would usually leave the dosage alone and test again after another week.
basically what you are trying to do it figure out how much Ca you system is using. If you keep increasing the dosage amount because you are measuring below where you want, you can way over shoot your target. Thats why i like to take it slow, if the measurements are heading towards where i want them, i usually sit back see how high up the dosing im at is able to get me.