Reefvet
New member
The potassium could be slightly higher and same with iodine, however i think adding a little potassium iodide would solve that issue. magnesium is also slightly lower, calcium and alk seem more or less just right.
In the 20+ years that I've been growing SPS I've never measured potassium and I've never worried about iodine. I've used every salt named in this thread and I've grown SPS successfully with all of them. I did start using a Kalk drip the first year I started with SPS
In an 18 with a real water volume of what, maybe 14 gals, you should be able to use IO or one of the other basic salts with great success. Do small water changes weekly, say 2 gals and drip kalk for top off. Alkalinity stability is the key.