Water changes.
I have had issues with IO salt for the last six months, no one else seems to have them, but mine mixes very low in CA and very high in ALK. When I mix water for a waterchange, I add Turbo calcium to the newly mixed water until the parameters are where I want them. The thing is, it's twofold. Turbo calcium is a dry form of calcium chloride, calcium chloride, it doesed quickly in large (relatively speaking) doses, raise CA and depletes ALK. So for a 5 gallon batch of new SW, I add 3/8 teaspoon of Turbo Calcium.
Once you get the params of the new SW where you want them, it is a matter of changing water with the good params frequently until the params of the tank are where you want them.