Drastic TDS increase???

[Mike]

Hey guys... Erik H. posted in another thread earlier that for some reason his TDS reading has shot up. He lives right around the corner from us and now our TDS reading has jumped up to like 90+ on the output... sometimes the output reads higher than the input??? I backflushed the unit and it did not seem to make any difference.

Anyone with any thoughts?

[CoryDude]

Is this reading after the DI canister? Mine had a dramatic increase a few weeks back, but it was because the ro membrane was going bad. I know that tds readings after the DI canister can shoot up dramatically, because the di resin is spent and it starts releasing silcates and stuff back into the output water.

[ErikH]

RO Membrane was my problem. Should come out of the RO membrane at less that 30 IIRC.

[Big_Pun]

not trying to be smart arse but has any of the tubing been disconnected and the waste water line mixed up. I've done that before

[CoryDude]

Hey Mike, if it is the ro membrane, I picked up one at Home Depot for for $50, and I'm getting almost a 98% rejection rate and about 40 gallons a day of useable water.

My problem was that I did't change the carbon block on a regular basis and what little chlorine that made it through, damaged the ro membrane pretty fast.

[corydrysdale]

Im running a RO/DI unit and really dont want to encounter any of these problems. Right now, Im running about 254 going in and 1 coming out. Sometimes it's hard to determine when to change the filters , without knowing how many gallons of water have been thru it. Are the monitors that you can get at BRS a good investment in monitoring the volume of water that passes through each canister and alerting you when you should change it or is it just cheaper watching the signs of your TDS output and changing stuff when you see the numbers shoot up....but then again, wouldnt that be a little too late. Anyone running one of these monitors?

[ErikH]

I have an in and out monitor, which I use to monitor everywhere! After the RO membrane is really a good place to keep it. Mine goes through three stages of DI, so it is definitely 0 coming out, that is a given. A good rule of thumb is to replace your carbon and sediment. I buy new ones every other month.

[BuckeyeHydro]

A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the useable life of these two filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. This is your indication one or both of the filters is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. A good 0.5 micron carbon block for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. Some original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons.

Regarding your RO membrane and DI resin, use your TDS meter to measure, record, and track the TDS (expressed in parts per million) in three places:
1. Tap water
2. After the RO but before the DI
3. After the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 parts per million (ppm). Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block filter (collectively called “prefilters”) do very little to remove dissolved solids. So with your tap water at 400 ppm, you can measure the water at the “in” port on your RO housing and you'll see it is still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce less purified water (aka “permeate”), but have a higher rejection rate (96 to 98%). The life span of a RO membrane is dependant upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the total dissolved solids (TDS) in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce less water as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the 40 ppm water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm, you know that your resin needs to be replaced. Sometimes people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty” water. This will exhaust the resin quicker than would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!
Russ