If you don't want to run a calcium reactor, then buy a doser. You don't need a 3 head doser if you don't want to fork out the cash. I used the Drew's Dosers from BRS on digital timers for years without a hitch. You could get away with just one for alkalinity if you really want, and add another for calcium later when you're going through more. The corals don't mind the calcium swing so much, but the alkalinity swing will kill you.
What kits are you using to test nitrate and phosphate? I'm not sure I believe they are "zero" by looking at your corals. IMO, those corals do not look starved at all. They look mad about something though. I'm not convinced that the alkalinity is causing the STN for you though because I don't believe that your NO3 and PO4 are "zero". The SPS can handle more alkalinity swing if the nutrients are higher.
Those look like cell phone pics. When you take pics, turn the blue channel off and set your phone camera's white balance to "cloudy" and you'll be able to get much better pics.