I switched from Prime to Safe. I don't pre-mix it.
I make sure to occasionally weigh a dose so that I remind myself how much to add.
Here's why:
Although it is difficult to overdose, it IS possible to do, which I did a few months back. There was sort-of a cascade of bad decisions on my part....I had a partially-filled (less than half-full) 10 gal tank that I was using to hold some fish before the Feb meeting. To start with, I was using way to big a scoop for 10 gal, and it wasn't even a full 10 gal, and I forgot whether I had even dosed it, so I did it again just in case, with another way to big scoop. Anyhow....way overdosed what ended up being probably only 3 or 4 gal of water.
What happens when you overdose, you might ask.....I did some searching and it turns out that it pulls the O2 out of the water. I suffocated my fish.
Chris' lesson learned: Slow down. Measure. If in doubt, start over. (and I work in a lab...you'd think I would apply these skills at home!)