I bought some of that for an ich problem I had a couple months ago. My fish were going down hill fast, and I had to have a treatment NOW. Since the situation was deteriorating so rapidly, I wanted a copper treatment, since (from what I've read) it's the only sure cure. I didn't want to chance experimenting with something that MAY work.
CopperSafe is a chelated form of copper, and that's all the store had in the way of copper treatments, so I bought it. They didn't, however have a chelated copper test kit. It was Sunday night, and no other stores would be open by the time I got to them. I bought it with the intention of going out the next morning to get a test kit (you HAVE to have a test kit if you are going to treat with copper). I couldn't find a chelated copper test kit at any stores in my area after having visited 3, so I bought a copper salt medication (Copper(II) Sulfate), and a test kit for ionic copper, and switched to medicating with that form of copper. Worked like magic.
Just a friendly reminder... don't dose a tank that houses inverts with copper, or you'll be saying "bye-bye" to all of them.
The following is my speculation on CopperSafe (I have a decent knowledge of chemistry (I work as a research technician in a chemical research lab)):
CopperSafe has it's copper chelated (think of "chelated" as meaning "enclosed in a larger molecule") in EDTA (a common chelating agent). Ultimately, the copper would be released from the EDTA in it's ionic form (which is what's required to kill the ich), but it would be released slowly as compared to a salt solution (copper(II) sulfate). If your fish are on their death bed, I would opt for the salt solution, as the copper ions will instantly be available as opposed to the slow release of the chelated form. The advantage of the chelated form is that if you are forgetful about dosing the tank, the chelated form will be more forgiving. If your fish look like they are just a little sick, and are not on their death bed, CopperSafe should work just as well in the long run. You should remove any carbon filter you have during either treatment, but especially make sure that you remove it if you go the CopperSafe route.
Like I said... the above is my speculation. Don't take any of it as "set-in-stone" fact. Good luck.
