Hello,
The 100mL bag of Purigen is about 3" wide x 4" in length, and it is about 1" thick. As far as the regeneration process goes, the dechlorination step and the buffer step are two different things. You want to soak it in some type of water conditioner to get rid of any residual chlorine from the bleaching process; then, if it is a freshwater system, you will want to soak it in a buffer that will lower the pH (bleach has an extremely high pH).
As for the products mentioned in the instructions, ChlorGuard and Prime are both dechlorinators/ water conditioners, while Discus Buffer, Neutral Regulator, and Acid Buffer are all buffers. You still want to soak the resin for 8 hours in dechlorinator, but for freshwater tanks, we recommend the buffering step, as well in order to bring the pH closer to that of your tank. (You only need to soak it in the buffer for 4 hours.) You can use the API Tap Water Conditioner for the dechlorination step, however since this product does not contain any buffers, you will still need to follow-up with the buffering step for a freshwater tank. Hope this information helps, and please let us know if you have further questions.
