I like to keep it simple.
Now this is very general, but pretty accurate and easy. Soft coral will use virtually no calcium. LPS will use a little. SPS will use alot. I don't worry about the trace elements that are replenished by regular pwc's.
When a coral builds it's skeleton, the 3 major elements it uses from the water are calcium, carbonate(alk) and magnesium (I'm not a chemist, so those 3 may not be the proper technical names). I don't know the exact ratio they are used, but say if it uses 1 gram of calcium, it needs 3/4 gram of carbonate and 1/8 gram magnesium. This is why it's important to use a balanced supplement to dose. You want to add those back in the same proportion they are used. A calcium reactor will keep the ca in range and should hold alk, but it does not add mag.
The plan should be to try to keep your water as close to natural as possible, so you want about 410 ca, 9 dKH alk and 1350 mag. These are the only 3 things I regularly test for. Whatever salt you use, test a fresh batch and see what you need to adjust. Personally, I use Red Sea Coral Pro. Off the top of my head, I think a new batch tests out at 450 ca, 8.7 dKH and 1325 mag. When I get home I'll check the actually reading I have recorded for freshly mixed water. Here's a good
calculator to help figure out how much of what you may need.
@Ziggy: I saw the pics of your tank and it does indeed look great. I am not doubting anything you say, cause you got the pics to back it up, but I don't understand how you don't have to dose anything. You can actually test your ca on Monday, then again on Friday it will be the same? If that's the case, why setup a ca reactor?
I think you saw pics of my tank. I lose close to 10 ppm calcium every day and I dose aprox 3/4 cup of the homemade 2 part solution of ca and alk every day. If I tested on Monday at 420ppm, by Wed I'm down to 400. I dose about 1/2 cup of mag every 2 weeks or so.