I actually have a 5 gallon bucket of the good stuff from BRS, but have still just been working through the box from Target. I ran the cheap stuff before and everything was fine.
I'm not saying what I do is "the best" way to do things.
Yes, I just add some to the sump, in a separate are than where my return is, and it's very turbulent on that side with a small opening high up for transition of the water to the return area.
Todd
Killed my first coral in 1991, have tried to do better since. Always tricky.