Regardless of anything else, your source TDS is pretty low. This is the case for most of us in GA. There is no reason you are not seeing Zero TDS after the RO & before the DI within a half hour of the system running. The only reason for anything higher are these things in order of likelihood. Low water pressure <50psi, improper tubing connections, bad ASOV, prefilters needing replacing and lastly RO membrane needs replacing.
Think of the DI as a final polishing, it's not there to do any heavy lifting. That's what the RO membrane is for. Also silicates have a near neutral charge and can foul the DI without it changing color much. BRS has some great videos on all of this. With PSI they will err on the lower side for liability reasons though. The higher the PSI into the RO membrane the more efficient it will filter and less waste produced. If everything is hooked up and functioning right, at 70-80 PSI in a single membrane setup you will see zero TDS right after it within a half hour of operation.
If you or anyone else are ever up my way I'd be happy to show you my system.