Well....what do you want to keep your alk
level at? Personally, I never keep mine higher than 9 dKH
max. I shoot for 8 to 8.5. You don't really want to raise it more than 2 dKH
/day so depending on where you want it, you can start dosing now.
I think BRS has a calculator to figure out how much of their stuff you need to dose. It's probably based on Randy's Recipe 1, but I can't say for sure. If it is, you can use the Reef Chemistry calculator I link to previously.
PurpleUp is not a good calcium supplement. It's just ground up aragonite sand in a weak mixture of water and calcium chloride. I have no idea how much it would take to raise calcium. Does a whole bottle raise 100g of water 10ppm, or 50ppm or 500 ppm
? The only way to know is dump some in a see how much the calcium rose.