I would turn it back on. If you start changing more than one thing at a time, it gets really difficult to troubleshoot what the issue is. I normally try to change just one thing, and then wait a while, when I'm trying to figure things out.
7.0 for pH is really really low... but you knew that. The article I linked to only talked about minor shifts in pH... not ones like you're showing. What was your pH before you started using the reactor? Also... what brand of salt are you using.
Now that I reread your post... if you're switching from tap to RO/DI, I can see how that might effect your pH since the RO/DI water is stripped of everything. But I use DI water (0.0 TDS) which is the same, and I manage to keep my pH at 8.2-8.3 with weekly 10% water changes... so I know it's possible.