I have switched to mei Marine-Max. I used to use IO and think I previously voted \polled as such. However, I had been having problems with maintaining alkalinity. It seems thay when IO is initially mixed up and completely dissolved, the alkalinity will measure as OK. Test that same bucket a couple days later and it will have lost a lot of it's alkalinity just sitting there. mei doesn't do that. Furthermore, the results after changing to this salt were obvious and favorable. It is my new salt of choice.
This salt takes a little (well, a lot) longer to go completely into solution, even though it is the finest most pulverized salt mix I have seen. The elemental balance and buffer capacity of the resulting solution is superior to any salt I've used in the past. If you haven't tried this salt mix brand yet, and you see some at a lfs, buy it and try it! Remember, let it sit as much as 2 days b4 change.
Greg