Red Sea Coral Pro reads out well, as does the original and is MUCH cheaper than the Tropic Marin.
I have tested just about every salt billybeau1 has and I have come up with numbers almost dead on with the exception of Coralife and Oceanic read higher in Ca in my tests.
I personally don't care for IO and adding supplements to it... It is a waste of my time and a PITA. I would rather pay a couple $ more for Red Sea AND get a 200 gal mix.
RC has had SO many issues as far as quality control and mixes that I am surprised so many people still use it.
All the reps that talked about the odiferous brown slime that was created by RC in the mixing vessels, blamed the consumer for lack of cleanliness, well how come it doesn't happen with other salts??
Supposedly the reformulated RC is better but IME not worth its weight in salt.