Tds readings

[underwaterdan]

So I have a brs Rodi unit and it has a tds reader in it. It has always read 001 or 000 I got suspicious of this and purchased a tds meter. It reads a tds of 053 for tap water and 024 for water exiting the Rodi. Is this acceptable or do I need to change something?

 

[AZDesertRat]

At a minimum you need a new DI cartridge but you need 3 TDS readings with the handheld TDS meter to know for sure.
Using a squeaky clean clear glass drinking water glass washed by hand in very hot water so it does not have any dishwasher soap residue or anti water spotting agents draw a glass of tap water and insert the handheld TDS meter. Let the reading stabilize, write it down then triple rinse the glass and meter in distilled water since you suspect the RO/DI is not 0 TDS. Next, disconnect the line from the RO to the DI and fill the glass with RO water before the DI. Insert the meter, let it stabilize, write it down and again triple rinse the glass and meter in distilled water. Finally hook the DI back up and draw a glass of RO/DI water and repeat the testing, documenting and triple rinsing. Cap the meter and turn the glassupside down so they stay clean for next time.
What are the 3 TDS readings? Since the RO does 90-98% of the work this reading is critical. You use it to calculate your rejection rate or membranes removal efficiency.

 

[underwaterdan]

Thanks. I realized that I have had my membranes for over a year. And doing 35 gallon water changes every other week plus ato water. So I am assuming that's the problem. I wish it was better.

 

[FL_Reefer]

It's definitely the membrane if your getting numbers like that. Change that sucker out and you should be good

 

[FishOfHex]

So I have a brs Rodi unit and it has a tds reader in it. It has always read 001 or 000 I got suspicious of this and purchased a tds meter. It reads a tds of 053 for tap water and 024 for water exiting the Rodi. Is this acceptable or do I need to change something?

It wouldn't be a bad idea to replace the membrane along with pre filters. I like to setup my dual TDS meter after the membrane before it goes into the DI resin that way i can get a better idea of when its time to change the pre filters.

 

[AZDesertRat]

You have no idea if it is the membrane or the DI at this point until you test the three TDS points I mentioned and make sure you test directly from the membrane and DI and not some storage or a dirty container. You could be throwing a good membrane away if you change it now or you could be throwing good DI resin at a bad RO membrane. Do the simple tests I mentioned and get back with the results. There is no reason an RO membrane can't last for 5-7 years or longer if taken care of. Mine is over 8 years old and still working at 99.4% efficiency.

Toss the inline TDS meter of use it only as a litmus paper type indicator test or quick reference, use the handheld TDS meter for accuracy. I'm afraid you are getting some questionable answers here so do some research before spening your hard earned money. Find out where you are at before throwing money at it blindly.

Besides the three TDS readings you really should know your exact measured waste ratio, your water temperature, water pressure and its good to know your water hardness. All of these have a bearing on how well your system will perform and how long it should last.

 

[FL_Reefer]

Can you please share how you get a membrane to last 8 years? I go through 1 a year. Also what is your TDS going in to it?

 

[FL_Reefer]

Also it's pretty easy to tell if your DI resin is at its end if it's the color changing kind and the smell sometimes. But yes you definitely need some reading to tell what's going bad

 

[AZDesertRat]

My tap TDS is anywhere between 550 and 850 depending on the sources and blend at the time. I do have a water softener which is the absolute best thing you can do for a RO membrane. RO membranes love softened water since it acts as pretreatment and does much of the work for them. Before the softener my membrane life was 24-30 months. Besides the softener I use only high quality, low micron, absolute or near absolute rated sediment and carbon block filters. The 0.2 or 0.5 micron absolute rated sediment filter protects the billions of tiny pores in the 0.5 micron carbon block so it can adsorb the chlorine and protect the RO membrane. If things don't get to the membrane it stays cleaner and lasts longer. I also firmly believe in keeping the waste ratio at the recommended rate for your source water, low waste systems do not work for everyone, in fact they don't work for most people period.
Color changing resins are usually unreliable. Often by the time you see the color change it is too late and you are passing weakly ionized substances into the finished water. Resin starts releasing weakly ionized things like phosphates, silicates and nitrates even before the resin is exhausted, and at much higher levels than in the original tap water since the resin has been storing these things up for hundreds of gallons so it is concentrated.
The smell you are experiencing is amines, kind of a fishy smell, and can be detected at very low levels. It is also noticable in fresh resin as well as exhausted resin so not a good indicator.
Nothing takes the place of a good ATC or auto temperature compensated handheld TDS meter. Inlines lack the accuracy, cannot be calibrated and are not truly temperature compensated so can be significantly off unless the air and water temperature are exactly the same, which is rarely the case. Inlines sense air temperature, if you were to cut the probes apart (I have done so) you will find the temp probe is in the fatter part of the IN or OUT probe behind the little rectangular window expose to room air. ATC handhelds have a metal probe that is immersed in the water being analyzed.

RO/DI is not really plug and play if you expect it to both perform well and to last for a long time. It doesn't take much testing or maintenance but just a few minutes can mean the difference between months or years when it comes to membrane and DI life. The more often you have to replace the membrane and DI the higher the cost per gallon of treated water. A little more investment in time and properly matched filters up front can mean many more gallon of treated water at a lower cost of operation since thye require less frequent replacements. Things like 5 or 10 micon nominal rated sediment filters are about as effective at protecting the carbon and membrane as a screen door. Did you know you can see 40 microns with the unaided human eye? Whis protects better, 0.5 microns or 10 microns? For the couple $$ extra I will opt for the better filters every time and save the higher cost membrane and DI.

 

[FL_Reefer]

Right I get and understand how all of this works, not new at this at all, and not trying to be a d..., so please don't think so. I have always used good quality products because let face it, your fresh water is the beginning of good water quality. I still can't get my membrane to last more than maybe 14-16 months at most. My water comes in at 350-380 TDS and comes out at 0. Do you think it's you water softer pre treating your water before it gets to your RO that is making it last that long?

 

[AZDesertRat]

I know you are trying to be better informed, that is why this forum exists and why subject matter experts like myself take the time to help others.
As I mentioned, a water softener is the absolute best thing you can do for an RO membrane. In fact all membrane manufacturers recommend soft water, their test reports are all done using softened water, and most of not all will not honor a warranty claim if softened water was not used. This is at the manufacturers level, individual vendors may have different warranties or guarantees but all will recommend a softener.

You say you use quality products, exactly what are you using for sediment and carbon filters (micron ranges and absolute, near absolute or nominal rated?) and how often to you monitor their effectiveness using things like an inline pressure gauge and a low range chlorine test kit and how often do you change them and disinfect your RO/DI system? Once the carbon is fouled with particulates or colloidal materials it allows chlorine to eat the membrane and they fail. Why are you changing the membrane, is the RO only TDS going up (poor rejection rate), or is the GPD going down (fouled or plugged membrane) or both? Just because the OUT probe on an inline TDS meter starts going up doesn't necessarily mean the RO membrane is bad, it could be the DI resin blend, the way it was packed, whethere it is mounted vertically or horizontally or how fresh it is. DI has a very short shelf life if not vacuum sealed in mylar foil bags and stored in the refrigerator or if has been opened and only partially used like with bulk resins and not resealed with a vacuum sealer and stuck in the fridge.

Another extremely important factor is the waste ratio. Have you measured your actual waste ratio to ensure it is at close to 4:1 waste to good? With 350-380 unsoftened tap water it should be at least 3.5:1 to 4:1. What about your water pressure and water temperature? Colder water actually treats better than warmer water and the 77 degrees you see all the time in reports is just a number picked out of thin air to compare one membrane against another, it is by no means the optimal temperature. Your DI will last longer with colder water.

 

[FL_Reefer]

Let me look exactly what I'm using when I get home from work and I get back with Ya. Thanks for the info bud

 

[FL_Reefer]

I looked at my sediment filter and its a 1 micro that I've been using and to be honest I really haven't noticed a difference with the carbon filters that I have bought so I get the CTOP 2510-10 if that makes any sense to you . Also I haven't really measured the waste water ratio coming out cause it goes into my planting beds on the side of the house but I will measure it cause now I'm curious, same with temperatures. I didn't know that came into play. I live in FL so the temp of the water will change but mostly I would say it's within 75-80 if I took a guess.

 

[AZDesertRat]

Looks like you are using a 10 micron carbon block. The 2510 means it is a nominal 2.5" diameter x 10" long and the -10 more than likely means it is 10 microns so very very coarse and with little chlorine adsorption capability. If you make much water at all they should be changed frequently if you have chlorinated water. For comparison, a 0.5 or 0.6 micron sediment filter is capable of removing chlorine from 20,000 gallons of normally chlorinated water if they are protected by an equal sized or smaller rated sediment filter. A 1 micron carbon is good for around 12,000 gallons, 5 micron around 6,000 gallons and 10 micron more like 3,000 total gallons. Remember all water including the waste goes through the carbon block so at the industry standard 4:1 waste ratio a 10 micron carbon could be exhausted at 600 treated gallons while a 0.5 micron lasts 4,000 treated gallons, about 6.6 times as long as the 10 micron for only a couple $$ more per cartridge!

Not all RO/DI systems are the same and some are much better than others for the same initial investment but save a ton of money in the long run and give you better water quality too. I look at the best water quality for the lowest cost per gallon treated so shop very wisely. What looks like a good deal often is not.

 

[FL_Reefer]

Cool thanks for the info bud, Ya I'm definitely changing it out before the 600 gallon mark but will keep that info in mind when it's time to change it out. Thanks again. Also could you shed some light on how you sterilize your RO/DI system? This is something I probably should be doing but have not. I think I'm going to by a hand held TDS meter just to be safe aswell

 

[AZDesertRat]

Do a search with my username and disinfection and it will bring up dozens of threads where I talk about disinfection.
For handheld TDS meters make sure it is ATC compensated such as the HM Digital TDS-3, TDS-4TM or AP-1 which should all be $25-$30. If you want greater low end accuracy I prefer and use the COM-100 which is more like $60 but reads down to tenths of a ppm TDS. I have an AP-1 as a backup and have owned and liked the other two also.
Another thing about carbon blocks is if you have chloramines a single 0.5, 0.6 or 1 micron block is more than sufficient for removing the chlorine portion and breaking the bond with the ammonia which is removed by the RO and polished off by the DI, not the carbon. A 5 or 10 micron carbon will not do this.

 

[FL_Reefer]

Thanks for the great info, I appreciate it bud!