After years of using Red Sea, for twice the cost of Instant Ocean, I think I am going to try to switch to IO. All salts mix a big gritty, except for Tropic Marin, in my experience. BUT, TM is almost 3x as much as IO and IO is half as much as Red Sea. I run an auto water changes system, so go through a great deal of salt. All salts are pretty good these days. Best to look at the levels of each individual salt after mixing at your desired SG, go with what matches your goals and stick with it. Pretty much can't go wrong with most brands out there.
Hope that helps.