High TDS in RO/DI Water

[sue1403]

We installed an RO/DI system about 3 months ago. Initially the TDS readings were zero, recently a test of the RO water read 254ppm. I've ordered new filters just to be safe but the system is new and our tank is 65 gallon so we're not using a ton of water. Any advice?

[AquaRick]

Was the rodi system new or did you buy it used? What is the TDS reading of your tap? If you have really bad water, it's not uncommon for filters to go out after a couple months.

[sue1403]

Thanks.......the system was new. Our tap water reads ~274ppm

[AquaRick]

It seems to me that 2 months is an awfully short amount of time to go from 274 tap to 254 rodi. When you first used your unit was the TDS reading of your rodi water 0?

[sue1403]

Yes, after we installed it the readings were zero. I didn't really test it again until recently, when I got the 254ppm, we flushed the system and the TDS went down to 60, but was moving around quite a bit and never went lower than 60ppm. The pH in our tank is 8.2.

[AquaRick]

I called a friend with a bit higher tds on their tap than you. They recommended to flush the system each week or each time you use the rodi unit. He said he was able to make the filters last a bit longer that way. Apparently too much crud was accumulating in the sediment filter and ended up ruining the others.

Maybe some other folks with high tds tap can chime in as well.

[Gti_Leo]

i bet the RO membrain has a rip in it, do you have a carbon pre filter? i'm sure you do but chlorine is a known enemy to RO membrains and if your local municipality uses a higher concentration of chlorine that may be the cause or it may just be a poormembrain, either way change out your pre fillters and RO mambrain and you should be good, if it happens again you may need and extra pre fiulter stage, a granulated carbon and a carbon block, to help filter out whatever is harming the membrain

[sue1403]

Yes, we've got a carbon prefilter, but you are right, our community water has alot of chlorine in it, (I can smell it). I've got new filters on the way and will install a second prefilter. Will make sure we keep extras on hand. Thank y'all so much for the help.

[mr_X]

I change out my prefilters and carbon block every 3 months it seems, but my R.O. filter I do about every 8 months.

[GottfriedMind]

If you're pretreating your water with a water softener (and an iron filter, if on a well with high levels of iron) your pre and post filter should only need changed once a year, provided your pre-treatment equipment is working properly, and sized properly.

Reverse osmosis systems that aren't used enough have the inherent tendency to a condition known as "TDS Creep". Dissolved solids will actually work their way back past the membrane into the inner workings of the reverse osmosis system. When the reverse osmosis system is used the next time, either by opening a drinking water faucet, or, in your case, opening a valve up for make-up water, those dissolved solids work their way into your holding tank. Over time, those dissolved solids build up in the holding tank.

By completely flushing your system once a week, you'll accomplish some positive results in your product water. 1) You'll greatly decrease the TDS content of the water in your storage. 2) You'll extend the life of your membrane by cleansing the outside surface of any mineralization that may start occurring.

Finally, IMO, 65 gals. is an awfully big holding tank, if it is a reverse osmosis tank....(With an air bladder....) If it's a atmospheric tank with a float, I'd completely flush the R/O to drain, and then open the valve to allow the atmospheric tank to fill up.

More on TDS Creep here: Reef Addicts - RO/DI TDS Creep - is it worthy of concern?