Hello, everyone! I've been trying to revive my ten gallon tank, so I got some Prime. How do I use it? It says to use one capful for 50 gallons, should I just guess where a fifth of the cap is? Also, how should I put it in, just dump it straight into the tank? Should I add it to the water when I do water changes... it seems really annoying to try to guess where even less than a fifth of the cap is. How should I do this?!