Move your IN probe to the tap water side for a few minutes and see what your tap water TDS is. This is a critical piece of information needed to calculate the RO rejection rate or removal efficiency which tells you if the membrane is doing what it should be or if you are relying more heavily on expensive DI replacements.
This is one raseon I dislike inline meters, they are limited to two places, usually post RO and post DI and to troubleshoot a RO/DI system you need three readings not two. With a handheld you can test all three plus your ATO storage, the LFS, you buddies, bottled water, etc.
You will see elevated TDS when you first start making water due to the TDS creep in the membrane. When you shut a RO off, the untreated tap water osmoses or migrates to the treated side of the membrane and raises the TDS contained in the housing. It takes a bit to get rid of that initial water every time you start it back up. So called flush valves DO NOT take care of this since they are flushing the waste side and not the treated side of the membrane as many mistakenly believe.
Final questions (maybe) :
Wold yourecommend getting the high capacity cartrige (DI-SB-10HC), or would the standard one be enough. I'm wondering if the HC is more for someone who is making more RO than me. I probably make 90 gallons/month.
Also, if I buy a replacment memberane now (MEM-0090), can I just store it, or does it expire? I don't mind buying it now to save on shipping in case I need it.
I plan to but a TDS3 meter so that I can evaluate the performance of my system better.