Believe it or not, this question will probably stir up a LOT of arguments. Some people will post that they use Tropic Marin and that Instant Ocean caused massive Algae outbreaks and death of corals/fish. While others will post that they use Instant Ocean and that Tropic Marin caused massive Algae outbreaks and death of corals/fish. You will never really get a straight answer.
Now, for my answer...I have used Instant Ocean and Tropic Marin. I started with Instant Ocean and then switched to Tropic Marin after I read it was sooo much better. After months of using it, my corals didn't seem to look as good as they used to. I switched back to IO and months later my corals looked better again. Was it the salt? I have no idea...I actually doubt it was. The fact is, that most people that have changed salts usually swear by the one they were using when their tank looked its best. Usually, IMO, the tank looked better because of other factors. Maybe they changed the bulbs somewhere around that time...maybe the plugin air freshener in the room ran out and stopped putting chemicals into the tank...maybe they have just learned a lot more about their tank and are just taking better care of it. There are a million things other than salt that can affect it. I personally use Instant Ocean, and I'll tell you why. I haven't had any issues with it at all, and the thing I like about it most is that it disolves very well. The Tropic Marin I used didn't seem to disolve as quickly as the Intant Ocean, and I noticed that the Tropic Marin made my skin itch.