That is a good number. You are sitting at 97.5% so not bad. It is well within the manufacturers spec of 95% rejection rate. So now it depends on if you are OK with that number. I have the 99% rejection membrane and my tap is over 400 and my tds after the membrane is 4. This number effects how long your DI will last. My 4 will get me around 1100 gallons of 0 tds water from a regular sized DI filter. Your 10 tds will get you around 440 gallons of 0 tds water.Update I replaced all of my filters except the RO membranes they are about 2 years old. I changed how my Inline filter reads, so now I checked my source water IN and between the RO membrane and the DI filters.
So now 360 source water and 10 PPM out of the RO membranes, does this sound about right? I checked my DI with a handheld and it reads 0 PPM.