I say this because you said you were new....
The 2 cups of water you are topping off with should be non-salt water. You're replacing the water that has evaporated. You should not be adding salt in your top off water.
get used up by a tank at the same time. You should only attempt to move Ca
upward if you know exactly what your Alk
Some of the earlier advice is best. Do a big water change, then begin to move your Ca
upward using a 2 part (A/B) additive. Don't try to move Ca
on it's own unless you know exactly what effect you are having on Alk