I'm not sure what is meant by "checking right on the bucket", but I test the levels of most of the saltwater I make, each bucket individually, to make sure that the levels are within "normal parameters."
Two-part is the nickname for a dosing regimen consisting of magnesium chloride/magnesium sulfate, sodium (bi)carbonate, and calcium chloride (it's technically a 3-part).
The other people I found on Reef Central used a combination of limewater, 2-part, and/or calcium reactors. I used two part, and actually switched suppliers of the chemicals midway through having problems because I suspected the 2-part LONG before I suspected the salt. Changing the 2-part had no effect (in fact, I'm still using the same 2-part solution I made during that time with no ill effect). Scott at some point changed to a calcium reactor, though I don't know when.
If we try to suspect the 2-part solution...how is that more suspect than RSCP salt? At least RSCP salt has only a couple of suppliers locally...and then keeps track of batch numbers. I use baking soda (food grade purity...obtained through various grocery stores...small boxes to keep batch problems to a minimum). I can bet 99% that anyone else using baking soda to dose probably didn't get the same batch number as me. I use epsom salts (food grade purity...obtained through various grocery stores, small bags as well). Once again, I can bet pretty highly (although not as highly as baking soda since it isn't a product used as much) that no one else using that to dose had the same batch. My magnesium chloride came from both Buckeye Field Supply and Bulk Reef Supply. I can't speak for the BFS source, but I know that the BRS source came from a very large high purity source. I'm sure lots of people are using the same batch I am throughout the U.S. The calcium chloride came from BRS in two different batches...both of a high purity source. Once again, I'm sure lots of people are using the same batches there.
Now, statistically speaking, how likely is it that me and a few other people all had the exact same combination/batch at the same time of 2-part solution versus a bad batch of salt? There are so many variables in the 2-part solution that I find it extremely hard to believe we had the same batches of stuff...whereas we ALL were using RSCP.
As far as RSCP causing some sort of chemical reaction with two-part solution? Chemically, the only bad reaction that I know of that could possibly occur is the build-up of sulfates, but that's been proven to be negligible in an aquarium setting except over long periods of neglect. Regardless, I even quit dosing magnesium sulfate for a while to make sure that wasn't the problem. In fact, I quit dosing each thing at a different time to see which one could've been bad. The tank never recovered a bit while I wasn't dosing one versus the other.
The ONLY thing in common between all of us that I can find, was that IMMEDIATELY, after we changed salt brands, our tanks looked better.
I find it interesting how several people are determined to *prove* several people botched up somewhere else. We have no solid evidence one way or the other. I am not out to destroy Red Sea...and neither are the other people that lost their tanks or corals from this problem. My biggest question is why are some people so protective of a salt, especially when I never even received a courtesy reply saying, "We're sorry about your loss, but we have no reported problems"?
If your tank is performing fine on RSCP, great! If you're happy with it, stay with it! I used RSCP for about 1.5 years with great results. However, as soon as I started a new bucket, my tank immediately went downhill...and recovered upon changing to a different salt. Who knows, maybe I'll try it again some day in the future. The whole point of my previous thread about this was for BUYER AWARENESS.
Please keep in mind our intentions when we post about our experiences, and remember that we lost animals near and dear to ourselves.