TDS @ 1 - Should I be concerned?

[HaleMoana]

When do I need to change out my filters?

[Playa-1]

If you haven't already, I would go ahead and get your spare membrane and filters ordered. I wouldn't bother changing them out until it rises up to around 5 or 10 ppm.

[Flipper62]

If you are using a TDS meter...Like a COM-100, the TDS should read 0.0 to 0.3....0.3 is realy a true 0.0 TDS reading. A reading of 0.5 is still ok.....but when the TDS starts to read this... you should start looking into changing the filters

[otrlynn]

How do you know when to change the membrane and filters, as opposed to just changing out the DI resin???

[Dino]

I'd go through and test your source/tap TDS, post-RO TDS, and post-DI TDS. Make sure you're using a nice clean container when you're testing (I use a glass glass, and have had times when a little bit of residue in the bottom has thrown things off). Just to see what you all need. Membranes typically last for quite a while so unless you filter a LOT of water or its older the membrane is probably fine (your tap TDS and post RO TDS will tell you how well the membrane is working). So all you'll probably need is some DI resin and some new prefilters (they're cheap so you might as well change them while you have the floor all wet anyhow ).

Since its already starting to rise though you might as well go ahead and get the filter replacements because the DI is probably nearing the end of its life.

[Playa-1]

My understanding is to change the pre-filters every 6 months due to potential bacterial issues.

The RO membrane should be bringing the tds to 0 if it's working correctly. When the tds begins to rise on the output water then your membrane is on the decline.

The DI resin will likely need more frequent changing then the rest of the filters/media. I like the idea of the color changing DI resin so there is no question when it is spent.

I think it would also be wise to change any Activated Carbon that you may have in the pre-filters system at the same time the DI resin is replaced. This may help preserve the life of the DI resin.

If your not running DI resin then it would be wise to test your discharge water for Chlorine and/or Chloramine on a regular basis.

[AZDesertRat]

At 1 TDS its time to order a DI replacement. You want to change the Di when you first start to see anything other than 0 on a consistent basis. Normally you may get a spike when you first start making water but it settles back down, its when it stays above that 0 or 1 when you need to change it. The reason is DI releases weakly ionized substances like phosphates, nitrates and silicates even before it is exhausted and some of those don't read well on a TDS meter.
The prefilter and carbon should be replaced every 6 months like clockwork. They are there to protect the RO membrane and very little to absolutely no effect on TDS, a meter does you no good here so stick with 6 month intervals. Remember to disinfect the system when changing filters to keep it sanitary.
The membrane should last 3+ years providing you do the required pre and carbon filter changes and disinfect the system. The higher the quality filters you use the longer it will last. Its not unusual to find a Spectrapure system with a 10 year old membrane due to the high quality/low micron filters they use.
To determine when a membrane needs replaced you can use a TDS meter as one tool but others are the pressure gauge, thermometer and a measuring cup and watch or clock. One indication is TDS rising from the RO only before it hits the DI. Another is reduced production rate not attributable to a drop in home pressure or colder water temperature. When you are no longer getting good removal efficiency or rejection and DI replacements are eating you up, its time to swap membranes. Another is lower GPD due to plugging or fouling of the membrane. If you do not keep the waste ratio at 4:1 eventually it will catch up to you and the membrane will clog with salts and qit working. No amount of flushing in the world will cure this situation as they are caked on there.

One last recap, 6 months on prefilters and carbons with a disinfection at the same time. When TDS rises for DI and when production slows or RO only TDS rises for the membrane.

[otrlynn]

AZDesertRat, how do you "disinfect" and what product do you suggest for this process?

[abulgin]

bleach.

[AZDesertRat]

If you can catch the search function when it is not busy, I have posted directions hundreds of times and never thought to save it as a word document so I can reuse it. Search my user name and disinfect or disinfection and it should come up. Its easy to do and takes about 5 minutes start to finish.

[AZDesertRat]

I found one of my old posts and saved it!

When changing filters, remove the prefilter and carbon housings and toss the old filters, add 3 tablespoons of regular unscented bleach to the prefilter housing only then screw the empty housings back on. Now, very important , disconnect the line going from the last carbon up to the RO membrane housing at the membrane end and stick the line in a bucket or the sink. If its not long enough you can get a longer piece at the hardware for about 50 cents.
Turn the water supply back on and let the housings fill until you start to get water out of the line. Shut the water off and let things soak for a few minutes. Its important to note here that bleach is a very strong chlorine solution, 5% bleach is 50,000 parts per million so more is not better in this case, only 3 spoons and no more.
Now turn the water back on and let the water drain out the line for a few minutes or until the bleach smell has gone away. Turn things off, dump the water and install the new filters and while the line is still disconnected turn it on and bleed any wate rand air out of the system before hooking the line back up and you are done. This also flushes the new filters to remove any carbon dust or fines so they don't get to the membrane.

[otrlynn]

Thanks so much for saving me the search AZDesertRat! I saved your answer and will put it to use. HaleMoana, I think I highjacked your thread a bit...hopefully you learned too...