Crystal Sea bio-assay is cheaper than I.O. That's the sole reason that Dr. Mac switched to it; coincidentally around the time when Shimek's article came out and lots of people switched. As far as evaluating the benefit of these different salts with regards to the metal concentrations, I think you'd have to use one for several years to really tell. This is because Shimek's assertion is that I.O. has an elevated level of trace metals, which build up in a system over time and cause mortality in invertebrate larvae. This, if true, would cause a DSB to stop functioning or at least not function as well.

To try a salt for, say, several months, and then say this one is better, etc... probably is missing the point. Certainly you could say "I like such and such about this salt or that" but I don't think you could really tell if Shimek's assertions are true until the system has been running for a long time. But, I would say since I switched to bio-assay I have noticed an apparent increase in mysid shrimp and amphipods in my refugium, but it's just an observation. It definitely mixes to a higher ph for me than I.O. did, though, and I like the smell. To me, I.O. has kind of a "chlorine" smell to it when mixed, but bio-assay has a much milder smell. As far as the compatibility issue goes, there was maybe the longest thread on R.C. ever on this topic, like several hundred postings and all kinds of theories and assertions. The most plausible one, if I remember right, was that the interaction of I.O. and bio-assay caused a release of copper (from the I.O.) due to weakening the chemical bond that keeps the copper in I.O. from entering the water as a toxic ion.