Which RODI part needs to be replaced first?

I have had my tank up and running now for about 4-5 months and have been doing regular water changes and also a 1-3 gallon top off everyday. I occasionaly check my RODI water with my TDS meter and it normally reads zero. I just tested it a few days ago and now its reading 10. I was wondering which cartridge or whatever needs to be replaced first. My sediment one is looking kind of light brown in color. Here is a pic of my setup - the resin is not mounted on top like in the pic - I changed that before it ever got used much. Thanks for reading and in advance for the help.

 

The prefilter and carbon(s) need to be replaced every 6 months and the system should be disinfected at this time.
The RO membrane should last 3+/- years if you follow the above recommendations.
The DI resin is dependent on how well your RO membrane is performing and how much water you make. I change DI resin when I very first start to see any TDS above 0 on a regular basis.

Do you check TDS at the three spots needed to troubleshoot your system? That is tap water TDS, RO only TDS before the DI and the final RO/DI TDS. You MUST have these three readings to know how your system is doing and if the membrane and/or DI need replacing. The prefilter and carbon have very little to absolutely no effect on TDS, they are there to protect the membrane which is the workhorse of any RO or RO/DI system.

Get the three readings and lets see where your problem lies. It may just be DI resin that needs replacing or it could be both the membrane and DI, in either case the prefilter and carbon(s) are due for replacement in about a month and the system needs to be disinfected, a 5 minute process that is very easy.

 

Wow, very thankful you took your time and let me know all of this. I will go and do these tests and post back up with my results in a little bit.

 

How do you disinfect the membrane? My unit is now 6 months old and I have the replacement filters already to install, but this is the first I have seen about disinfecting the membrane.

thanks

 

A couple of quick tips on TDS meter usage.
I always use a nice clean clear glass drinking water glass with absolutely no soap residue or water spots which can skew results. Initially I was the glass in super hot water by hand rather than a dishwasher which can leave soap residue, water spots or anti spotting agent films on the glass and then dry it carefully.
I first draw a glass of tap water and stick the TDS meter in the water for a bit to let the readings stabilize. I write it down then triple rinse both the glass and meter in RO/DI or distilled water so both are squeaky clean.
Next I either disconnect the line between the RO and DI or I spent a couple $$ and installed a speed fit tee and ball valve so I can draw samples without disconecting or removing anything. Again fill the glass with RO only water, insert the meter and let the readings stabilize. Record the readings, triple rinse the glass and meter and do the same with the final or RO/DI water and do a final triple rinse, cap the meter and turn the glass upside down to keep any dust, salt spray etc out so its clean for next time.

Your RO only reading should be somewhere about 96-98% less than the tap water TDS if the membarane is functioning correctly and of course the RO/DI should be 0 or very near that.

 

Ok, the results are tap water 298 RO 43 and Final 26
Not looking too good. I even recalibrated my TDS with the correct solution.

 

Remove the prefilter and carbon(s). Add 3 spoonfulls of regular unscented bleach to the first housing, no more than that as bleach is a very strong disinfectant, up to 50,000 ppm when fresh. Screw the empty housings back on. Now, VERY IMPORTANT, disconnect the 1/4" line that leads from the carbon filter up to the membrane housing at the membrane end and stick it in a bucket or the sink. Turn the water supply on slowly and let the housings fill completely until water starts to come out the disconnected tube. Shut the water oof and lets things sit for a few minutes. While you are waiting ponder this, the Centers for Disease Control in Atlanta has determined that a chlorine solution of only 0.5 ppm or mg/L will kill almost any bacteria or virus known to man with a 5 minute contact time, thats on 0.5 ppm and undiluted bleach is 50,000 ppm so thats why I say more is not better.
Turn the water back on and flush until any chlorine odor has dissipated. Remove the first empty housing and install the prefilter, flush it to waste again for a minute or two to flush out any binders, dust of glue from the construction of the filter. Now install the carbon(s) and again flush each one to waste to remove any traces of carbon fines or dust so it does not reach the RO membrane. Finally hook the 1/4" line back up and flush any trapped air out by rotating the unit around in your hands and you are ready for another 6 months. Always change filters at least every 6 months.
If you are replacing the RO membrane too you can do the whole system with the membrane removed then install the new components one at a time flushing each in turn before installing the new DI resin and flushing it last.

 

How long did you let the RO run? You may be seeing the effects of TDS creep if it did not run long enough.
Do you have a pressure tank? Where did you sample the RO only water from, hopefully directly from the membrane and not from a faucet or pressure tank?
How is your system plumbed, does the DI come directly off the RO or do you use RO water out of a pressure tank to feed the DI?

Another couple of questions:
1. What is your water pressure?
2. What is your water temperature?
3. What is your waste ratio, you can find this out using a measuring cup and watch or clock measuring the flow from the treated RO/DI line and from the waste line both for the same 1 minute or whatever timeframe.

 

Tap water 298?? Man..you have that thing workin' hard! Mine's 56 before it goes in

 

OK,I will do this - I may as well do the prefilter and carbons at the same time since that are almost due now anyway. Thanks a million you have been so helpful.