Re: Purigen during Cycling process
If you are aiming for a neutral pH, then I would go with the Neutral Regulator. Neutral Regulator is a phosphate-based buffer that will bring pH to 7.0 from above or below (I know you're trying to bring it up), and it will also hold that pH very stable. People who are keeping live plants generally want to steer clear of phosphate-based buffers, since excess phosphates can encourage algae growth, this the previous question about what type of tank you have.
Another benefit of Neutral Regulator is that it will fully condition your water as well as serving as a buffer, and you will therefore not need to use the Prime in conjunction with it. Because you're not keeping live plants, I also don't really see a need to use RO water for pH control, as simply using Neutral Regulator should suffice for your water conditioning and buffering needs. Hope this helps!