Calc, alk and mag - randy's slop made from whatever quality grade of chemical I can buy in quantities that make all and sundry believe I'm running a drug lab. It's on a dosing pump on my display system. It goes through a fair bit of the stuff despite being light on the SPS. Usually a lot of small doses throughout the day rather than bigger, less frequent doses.
Anything else probably comes in a Brightwell bottle - KoralColor, Zooplanktos-S, Microvore, Reef Snow,Vitramin-C, Restor, and whatever else I've forgotten. Combinations of which, when and how much vary greatly. The frag system sometimes gets some of this, but at the moment is on a Red Sea diet while I try to replicate some results I've had in the past. Zooplanktos, Microvore and Reef Snow tend to be stuff I frequently throw in. The others are for specific uses. I had debated using their Lugols Solution as an additive for a while, but given its cost and the potential risk I've gone back to just using that as a dip.
Anything that gets added has some rational reason for going in - specifc corals that consume what it adds, potential growth benefit, colour benefits, third hand information from a guy who knows a guy who knows a guy that dosed something and his tank mutated into an ultra wanker grade SPS farm, etc. I tend to try different things as they're suggested to me and I see what happens. I can't even remember what half of them do any more. I worry about that when the bottle's empty :P Dave @ Deer Park is pretty good to talk to about Brightwell products, and @
K&J Aquatics carry a pretty good supply of their gear.