precise control over water re-mineralization

Question

I have been trying for, literally, decades, to get really good coffee.

I roasted for several years, and for two cups during that time, I reached absolute nirvana with coffee that tasted so good it literally changed my life. However, it was so hit and miss, I essentially gave up on it.

Now I'm desperately trying to be sure I'm doing the most that I can to do everything right to attempt to arrive at that taste with what I hope anyway, is recently roasted beans, though trying to locate a source of those, from a roaster that is willing to divulge the age of the roast (I am in a rural area, there is no "local" roaster I can form a relationship with) is proving difficult. Anyone who knows of such a mail order roaster, I would love to hear.

Starting with the basics, I am trying to get the water exactly right as per the SCAA recommendations. If I understand those correctly, it should be chemical free water, with a TDS level of around 150.

I purchased an ISpring RO filter system, with a re-mineralization filter. It does it's job, though the TDS at the outlet turns out to be around 30-40 range. So, being an engineer, I assumed I could put 5 remineralization filters in series, and "of course" I'd end up with 5 * 30, or 150 TDS.

Hah !

Not even close, with five such filters it didn't increase the TDS at all. I can almost see why when I think about it.

So my question is: How can I get re-mineralization up to 150 TDS with my RO water filter.

Note that I'm aware of packets of minerals you can buy to add to water. I'm really looking for a "machine" solution, i.e., totally hands off yet extremely precise every time, without any sort of intervention other than turning on a tap. If there's no other solution, maybe I could build an automated "doser" to dump minerals in as the system calls for water. Maybe such a thing already exists ?

Thanks all for your help, and patience reading my question.

Nate