a hand held tds meter is far more useful than the mounted tds meters, i ended up purchasing from buckeye field supply
clear housings
1-micron poly depth sediment filter
0.6-micron, 20,000 gallon carbon block
Filmtec RO membrane (50, 75, 100, gpd) or Buckeye brand membrane (150 gpd )
aluminum bracket
pressure gauge and thermometer
housing wrench
drain saddle
6 feet of tubing for supply water, for drain line, and for purified water
handheld TDS3 TDS meter by HM Digital
RO flush valve
DI bypass valve.
$169