With that much coral and a clam you're going to need to start either dosing 2 part or pick up a calcium reactor... You might be able to pick up kalk reactor and increase your kalk but I'd just go with a two part system or a calcium reactor with quality media.
Like everybody else said go slow but you need to get that alk on the rise soon or your going to start losing corals.
The red sea test kits are actually great, just remove the silly little tips and just drip directly from the syringe and swirl between every drop it'll give you a plenty close measurement to know where you need to be.
Don't stress too much on chasing numbers, you'll drive yourself crazy... just get your tank up to a balanced level of alk and calcium in an acceptable range and let your corals tell you what they like and keep that mag up above 1300. I prefer Kent salt as well because of the higher mag, I never have to dose mag in either of my systems.