Filter Direct is the name of the company(distributor) on e-bay that a lot of us here bought from, dakar gave you the link. Basically you have a 5 micron sediment filter, 2 stage carbon filter. membrane and then a 2 stage DI filter. Thats a good set up for a RODI unit. It also has an automatic shut off which will shut the unit off(stops making waste water when the unit stops producing RODI water).And yes the TDS (total dissolved solids) meter measures the quality of the water. Zero is what you look for after the unit. As far as changing the various filters, that depends on how good or bad the water is going into the unit and how much you use it. That's were the meter comes in handy, it will tell you when it's time to change your DI media or membrane. You can get a visual on the filters.