I used to use reef crystals, but the ALK was just too high. I keep my ALK at around 8 dkh, and I had tested batches of reef crystals at 14!
I make 30g batches of water with IO every week. I just throw in about 200 mL or so of calcium and a bit of Mg and potassium for good measure and I'm good to go.
I struggle with keeping my ALK stable. It's usually hovering about 120 ppm, but I can not get it steady there for long. Sometimes will drop to 90 and then go up to 140 ppm. I have a feeling that my water changes with IO (which tests at about 11 dkh for me) is causing fluctuations. If I'm "too good" with my water changes, it'll run a bit high, and if I'm bad with it for that particular month, it'll run low.
I dose two-part to keep levels up, but since the salt I use is at a different ALK as my tank, I become too reliant on steady water changes to keep my ALK stable.
This is just what I am guessing. Maybe I'm just really bad at measuring stuff.
The main reason why I use IO is the fact that it is so easily attainable for me at a reasonable price. I don't want to not do a water change b/c I ran out of salt. I can pick up a box at the SPS store or at rainbow pets for the same price (or cheaper) than online. If salt is affordable, I'll be more likely to keep up with my water changes, or be more willing to toss out a bad batch (no "I got some rain water in my salt mix. Can I still use it?" conflicted questions from me).
But with my ALK swings, I'm debating if I should switch salts. I've been slowly seeing a very very slow STN-ing on my deepwater corals that is, quite frankly, ****ing me off. I can't quite figure it out. I'm guessing it's b/c of my unstable ALK. Milleporas, staghorns, torts and all non-acroporas are doing great, but I can't seem to keep an echinata alive for the life of me. They have been the bane of my reefing experience. What kills me though, is that the echinatas do GREAT in my tank for the first 6 months or so. I get stellar growth and gorgeous hues from them. And then BAM! I'll see a white patch on the base, that will slowly creep up. It usually takes a full month or two before I lose the whole frag/colony.
Sorry for the rant. I know you asked about the salt and I just went off on a silly little tangent.
Maybe I should buy this off of Diver's Den and see if I can break the curse!