I've got both brands here right now, guys, TM dissolves almost instantly and I have two bags of IO that both take forever to dissolve. This is the first time I've used IO. I got both bags of IO from the same place, and they've sat around for awhile, so maybe they are contaminated. Either way I buy the Tropic Marin for the supposed completeness of trace minerals and such. I am sure the IO is adequate though, and didn't mean to offend anyone, I was simply using that as an example of differences, however inaccurate it may be. Happy reefing!