In the process of changing as we speak. I had been using IO, but I am currently changing my 135 over to a reef, mostly LPS so I am switching to Tropic Marin for a minute and just picked up a few buckets to try. I used to use the Neo Marine years back when Stephen came out with his New Zeo system as well. Truth be told I walked away from salt 7 years ago due to a huge crash on my 300 when I was out of town for three days. I'm sure you've heard the stories over the years, but it took me 6 years to get over the loss.
The 135 is still fresh water, so I will be using this on the 300 FOWLR and I also have a 75 mini reef I call it just under way [two month cycle] where I will see how it does.
Lots of changes while I was away so not stuck on a brand just yet is the short answer.