Yea my source is 350+TDS 7.6 ph /2-3 kh and aprox 9 GH .
I mix my ro which without DI is aprox. 18 TDS with tap to get 75 -100 TDS.
Like I said when I used the PH pen it said my ro was 8+ which is not really possible as far as I know..The one time I tested my ro with my API liquid test it did not even read as high as lowest[under 7] on the api color chart ,so I don't even bother to figure it out..
Once I get something to work I don't mess with it or try to be overly meticulous.. TDS is all I care about for breeding the rams ..I test TDS even on my swordtail tanks which with the addition of wonder shells goes around 1100 TDS ! The PH due to wonder shells is actually driven down so I add baking soda to keep it in the 7 range...