I'm relatively new to this so take my statements with a grain of salt and perhaps a more experienced member here can confirm or deny what I've learned and experienced.
RO water should read with a TDS of 10ppm or less. At this level you will not provide the proper the trace elements. RO membranes will remove Calcium, Magnesium, Sodium, Iron, Manganese, Bicarbonate, Chloride, Sulfate, Nitrate and Carbonate. You can see many of these are needed by plants, not providing enough could cause you issues.
RO/DI water will should have a TDS of 0ppm. Your working with pure water that can be very unstable. No trace elements, no bicarbonate to offer any buffering against a PH crash.
Have you tested your water after your RO unit for TDS, GH, KH? If you have a super low TDS the PH, GH/KH test kits will not be accurate. But a low TDS may also indicate you need to reconstitute your water. I'm not sure at what PPM the API test kits can detect. I believe there is a chart that transfers DH to PPM somewhere on the API test kits but I never bothered to look.
After I reconstitute my water with GH booster and baking soda my TDS is around 160. I still continue to dose NPK and CSM+B (EI dosing). Im not familiar with the ferts you have chosen so I'm not sure what you are/aren't providing.
Water top offs for evaporation you want to use pure RO or DI water to prevent a buildup of TDS.
Then again if your plants are growing... don't fix it if it ain't broke!
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