HM Digital Handheld TDS Meter w/ Thermometer Here is a link to the TDS meter I use. This is the same meter I used when I installed/serviced RO units for a living. This meter also compensates for temp fluctuations like AZ is talking about. Flow Restrictor This is the flow restrictor or capillary tube that can be trimmed to dial in flow. I recommend replacing this whenever you replace your filters. They are cheap and it will improve the life of your membrane if you have nasty city water. Just a side note. You may want to check that the pressure gauge is working correctly. These types of gauges (or any gauge at that matter) will eventaully fail. I would hate for you to continue going crazy trying to get the pressure up when the gauge isn't working. The pressure gauge looks like it can be removed easily. Hook it straight to the water inlet line from the wall to make sure it's working (you may have already verified this in previous posts, if so I appologize).