Hi Joyce.
My understanding is that CDS can't legally be shipped in the US. I know of only one US based company that will ship CDS.
Personally, the only reason I make and use high concentration CDS is for topical use.
Since you are making overnight CDS (OCDS), to make higher concentration (ClO2 ppm) CDS just add fresh solutions to the reactor container and put that back in the receiver container holding the CDS you just made and process for another 12 hours. Keep doing that until you get what you want. As you are probably aware, at higher concentrations CDS can become unstable. Be sure to keep it cold and especially out of strong light.
Yes, the solution color can give you an indication of the ClO2 concentration, but not always.
This photo shows two OMMS (overnight MMSA) solutions that measure about the same ppm; 6400 ppm the left jar and 6500 for the right jar. I would have guessed the left jar was higher ppm, but it is really the same as the right jar. Different methods were used to make these OMMS solutions.
And yes, measuring ppm with LaMotte ClO2 test strips is a rough measurement tool, but better than nothing or a visual guess! I use both, but mostly use an eXact Photometer to measure small differences in concentration that could not be seen with LaMotte ClO2 test strips.
Regarding the so-called "stabilized" CDS, I have not seen any proof offered that adding MMSU to CDS will help retain ClO2 concentration. And I have also read that the purpose of adding MMSU to CDS is not to "stabilize" it at all, but instead it is supposed to increase the effectiveness of CDS. At least, that is someone's theory.
This link describes how well CDS can retain its ClO2 concentration after 6 months of storage at room temperature, not in a fridge.
g2cforum.org/index.php/list/cds-chlorine-dioxide-solution/26462-cds-long-term-storage
By the way, Scott (truthquester) will soon be publishing a report on OMMS in case anyone is wondering why we do that.