I think Returnofsid has an excellent point about the adaptability of corals. When subjected to swift changes in parameters, many of the more fragile species expire, although the apx. 20 species in my tank are tough enough to deal with near-instant .2-.3 point salinity fluctuations, and fluctuations between 2.3 and 2.6 on a longer time scale(they objected strongly to 2.7 though, but I received a Kenya tree frag once that was growing happily in water that tested so high it was off my salinity meter...)
If you want something that will be seriously affected by your test, I think you need delicate SPS ;->
If you haven't thought of it already, I'd suggest pre-bagged live sand for the tanks. IMO even cured wet live rock would be too hard to control the equality of. Perhaps dry live rock would work?
I read the most interesting study the other day of clownfish babies raised in acidified water, maybe you could try acidifying the water?
If you don't plan to keep it for more experiments, I would love to have your set-up when you are done. I'm a 1st-3rd grade teacher, and I'd love to set it up in my classroom and let the kids design experiments galore and publish the results on a class web page
I have two saltwater tanks at school right now - a little one for 'touching' and a larger mixed reef for looking. The kids absolutely love it, I love it, and it doesn't stink like small mammals, birds and rodents do