<a href=showthread.php?s=&postid=9477340#post9477340 target=_blank>Originally posted</a> by bustayanky
very good info. And for the TDS meter what's a good reading?
The TDS will help to measure two things, the quality of your water which if the unit has a DI cartridge the reading shall be zero as mentioned above and the DI carridge or resin shall be replaced when the reading is 1 to 2 ppm.
It is also useful to test the performance of the membrane by measuring the rejection rate.
Filmtec membranes of 75 gal/day or less when new shall have about 98% rejection rate and replaced when their rejection has fallen to the 90-93% range.
The rejection rate is calculated using the TDS at the input of the membrane TDSin (After the carbon filter) and comparing it to the TDS read in the product line after the membrane before the DI cartridge TDSout
%rejection = (TDSin - TDSout) x 100 / TDSin
so if the reading at the inlet is 230 ppm and at the output is 12 ppm that membrane has a rejection of 94.8% (230-12)x100/230
The TFC membranes are very sensitive to chlorine and get damaged by it so you need to insure that your carbon filter is removing all of it. To do so you will need a chlorine test kit (There are some very economical that use tables) to regularly test the water comming out of the carbon filter before the membrane. At the moment you detect any chlorine traces the carbon filter needs to be replaced.
Finally the sediment filter has to be repaced when the pressure drop between the tap and the membrane is 10 to 15 psi which indicate the filter is getting pluged with dirt.
