After all was done with our plumbing system, and the RO systems was OK, I decided to check our water quality. Our city has poor water with over 1000 ppm dissolved solids in the water (i.e., very hard water). The water in my RO tank tested at 9 ppm. The Ph of the water in the RO tank was 7.0. In the mixing tank, the Ph was 6.9.
Both are very acceptable, and within the range for growing orchids. According to several websites, orchids maximize the nutrient uptake when the water has a Ph of about 6.2 — or slightly acidic.