Gerald, according to the web site of the product, it is a phosphate buffer. I don't know what would be the final concentration, but I personally wouldn't increase the TDS. The components of phosphate buffers are parts of plant nutrients (PO4, K, Cl) and some Na, so if it is not at a high concentration, they shouldn't cause too much problem. But excess of P is probably not a good idea (for example, mycorrhizae association usually get broken by high P).
Also, I'm not sure where you got the idea of pH 7 is optimal for irrigation/fertigation water. I'm not saying pH is not important, but the pH environment of root is highly influenced by the potting media. So if you are trying to play with pH, you should pay attention to the pour-through pH than the fertigation pH. You can measure the pour-through pH by fertilizing normally, then after 30min or 1 hour, you can pour pure water (about 1/4 cup) and catch the water flowing out from the bottom.
There are experiments where some orchids like Phal hybrids can have no problem growing in media with pH of 3-4. See a related topic here:
https://www.orchidsforum.com/threads...thopsis.15197/
Similarly, water of pH isn't that important since most of us are probably adding fertilizer unless you are using water with super high TDS (pH of fertigation water is dominated by the fertilizer formula in most cases).