Any salt will grow coraline algae initially, no need to dose or select any particular salt for that purpose. Eventually, calcifying organisms such as coraline algae will deplete the calcium and alkalinity levels faster than your water changes can keep up with. This will slow growth. Growth will not stop- it will just slow down until the next water change. This is what happens in many FOWLR tanks.
If you want your coraline (or other calcifying organisms such as certain corals) to not be limited in their growth, you can either increase the volume of the water you change or your water change frequency. When this is not practical, most turn to supplementation such as two part.
I would not move to dosing 2 part until you confirm that your alkalinity is being depleted with regular water changes. Often in low use tanks such as your own, you only need to start dosing 2 part after 6-24 months, with over a year or two being pretty common. This would change if you were to add corals other than zoas and mushrooms that use a calcium carbonate skeleton such as some LPS and SPS corals.
