16 ppm OK for RO/DI output?

randL524 · 01/26/2007, 02:42 PM

Just purchased a TDS meter and checked my tap water (~143PPM) and the output from my used RO/DI unit which is at 16 ppm. I just ordered a new pre-filter. Am I OK or do I need to replace my membrane?

Waxxiemann · 01/26/2007, 02:45 PM

I'd replace the DI resin at the least and check it out after that.

16 is no good IMO. The memebranes usually last quite some time. You'll know it's going if you're loosing pressure.

MCary · 01/26/2007, 02:47 PM

That's a little high. I like to change my membrane if it goes over 10 ppm. Is your meter calibrated? What is the lower linear range of your meter?

Mike

Icefire · 01/26/2007, 05:30 PM

Change the DI resin.
Test the water without the DI, it's should be at 10-14ppm with new prefilter.

AZDesertRat · 01/26/2007, 06:14 PM

16 ppm is high for RO only even if your tap is only 143. Thats only 88% rejection. You want to be in the 96 to 99% range with RO only to maximize your DI resin life. A good rule of thumb is for every 2% you increase the RO membrane efficiency you double the life of the DI.
Using a squeaky clean glass drinking water glass with no soap residue or water spots first test your tap water TDS, triple rinse the glass and meter in distilled or DI water, test your RO only without DI and again triple rinse both then finally test your RO/DI and rinse a last time then turn the glass upside down for clean storage and cap the meter probe.
RO only should be 96 to 98% or more less than the tap water TDS so at 143 you should only be seeing 3 to 5 TDS. DI should easily be 0 indicated TDS.
Prefilters and carbons have very little effect on TDS, they are there to capyure suspended solids not dissolved solids. Chances are you need a new RO membrane but do the testing first. It may only be worn out DI resin which when used up starts to release the contaminants it has captured back into the treated water. Never let DI get over maybe 2 or 3 or it will start to leach and possibly cause worse water conditions than waht your tap started out to begin with. Do not rely on color changing resin either as it is a really poor indicator. Always use a handheld TDS meter.

WaterKeeper · 01/26/2007, 06:15 PM

Yes, change the DI cartridge not the RO membrane.

WaterKeeper · 01/26/2007, 06:17 PM

I thought my solution was less drastic Rat.

AZDesertRat · 01/26/2007, 06:31 PM

RandL524, I think the steps I have suggested will help you pinpoint your problem(s) before spending any money. If it turns out its only the DI cartridge thats great and less costly, but if you buy a new DI and it turns out the membrane is also bad and passing high TDS to the DI you will have worn out a new DI cartridge needlessly. Identify the problem first and it will probably cost you less in the long run. Without knowing what the RO only TDS is its impossible to know what to buy. Cross your fingers its only the DI and if you are really lucky your unit has a refillable DI cartridge and you can buy a bag of bulk resin and save even more money than having to buy a whole new cartridge.

WaterKeeper · 01/26/2007, 06:35 PM

I was kind of thinking that the 16 reading was off the DI stage but that may be wrong. Anyhow, I need to be nice to a guy from Connecticut even thought they deported me to Ohio three decades ago.

drummereef · 01/26/2007, 08:08 PM

If you are testing after the DI stage you need to replace the resin. You should be getting 0's after the DI.

AZDesertRat · 01/26/2007, 08:22 PM

Again do not replace the resin without first testing the RO only TDS. If its bad and passing high TDS on to the DI you will waste a cartridge in a hurry. Yes you probably need new resin but why contaminate it if you do not need to?
If your RO is bad you could be passing 143 ppm TDS to the DI and a brand spanking new 16 oz DI cartrdge would last about 14 gallons at that level.

randL524 · 01/27/2007, 04:08 PM

OK. My tap (using the triple rinsing clean glass technique - thank you Rat) was 126 ppm. the RO output (I revmoved the mxed-bed resin cartridge, rinsed the empty cartridge with distilled water and then let it fill) was 8 ppm, for a 94% RO efficiency. Not where it should be, but is it acceptable? Clearly the resin needs to be replaced. Do I spring for the $30 - $40 for a enw one, or can I refill the inner cartridge or recharge the resin...?

AZDesertRat · 01/27/2007, 04:19 PM

Looks like the membrane is still acceptable given your low tap water TDS. In my case with a tap TDS of over 800 I would go through resin like crazy with a 94% rejection membrane as it would be a TDS of about 50 going to the DI instead of my normal 7 or 8 from my 99.1% rejection rate membrane. You can see where a few % makes a big difference.
If you have a vertical 10" canister type DI, I would get a refillable cartridge and a few bulk refills from one of the RC sponsors if the cartridge you have now is not refillable. It will probably cost you about the same as buying a throw away cartridge would locally.
I think www.thefilterguys.biz had a good deal last time I was shopping for resin. You might also check www.buckeyefieldsupply.com and www.purelyh2o.com though and compare.
Glad the membrane is OK as that will ave you some money for awhile longer anyway. Once the efficiency starts droping more though you might want to look into replacing it so DI will last longer, its a trade off, less money now on membrane but slightly decreased DI life or more money now on membrane and increased DI life.

WaterKeeper · 01/27/2007, 04:23 PM

I think why we disagreed slightly on this one Rat is you forgot that good old Dowex ion exchange resin tends to leach back ions when it become exhausted. This makes the TDS of the output of the train seem higher than the RO source water.

AZDesertRat · 01/27/2007, 04:49 PM

I just didn't want to see him spend money on a new DI cartridge without first checking the membrane. That would be like throwing good money after bad since the resin would be exhausted quickly. I have seen this happen a few times and then they wonder why their DI only lasted 2 weeks. An RO/DI is a complete system and depends on every component to work effectively and cost efficiently. Poor or worn out prefilters and carbons shorten the life and decrease the efficiency of the membrane which in turn shortens the life and lower the effectiveness of the DI. It all has to work together! Thats like playing nice together as I tell the Grandkids.

WaterKeeper · 01/27/2007, 05:26 PM

Oh, and I agree. It's just that a spent DI showing 16 ppm is pretty common even with an RO stream down around 3-5 ppm.

AZDesertRat · 01/27/2007, 05:55 PM

Absolutely, most people don't realize when a DI cartridge is exhausted it can quickly release contaminants at higher levels than are present even in the tap water. Once you start to see any elevated reading at all from the DI change it ASAP.

01/26/2007, 02:42 PM	#1
randL524 Registered Member Join Date: Jan 2007 Location: CT Posts: 18	16 ppm OK for RO/DI output? Just purchased a TDS meter and checked my tap water (~143PPM) and the output from my used RO/DI unit which is at 16 ppm. I just ordered a new pre-filter. Am I OK or do I need to replace my membrane?

01/26/2007, 02:45 PM	#2
Waxxiemann Registered Member Join Date: Feb 2006 Location: Winnipeg Posts: 2,364	I'd replace the DI resin at the least and check it out after that. 16 is no good IMO. The memebranes usually last quite some time. You'll know it's going if you're loosing pressure. __________________ "Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe." Albert Einstein

01/26/2007, 05:30 PM	#4
Icefire Seasoned reefer Join Date: Jan 2007 Location: In Quebec, Canada Posts: 3,653	Change the DI resin. Test the water without the DI, it's should be at 10-14ppm with new prefilter. __________________ Temp 80F, PH 8.5-8.0, Alk 6.8-7.2, Ca 430, Mg 1700, NO3 0-0.25, PO4 0.04, 34.4 PPT Lights @ 100% all others, 35% White Current Tank Info: 60g Cube, 120lbs live rocks, Hydra52 2x120W, 2 MP40+ 1 MP10 @ 70%, Phosban 550 GFO+Carbon, 200W Heater, SWC Skimmer, Kalk ATO, 150 gpd RODI

01/26/2007, 06:15 PM	#6
WaterKeeper Bogus Information Expert Join Date: Oct 2000 Location: SW Ohio Posts: 16,147	Yes, change the DI cartridge not the RO membrane. __________________ "Leading the information hungry reefer down the road to starvation" Tom Current Tank Info: 130 Now out of service and a 29

01/26/2007, 06:17 PM	#7
WaterKeeper Bogus Information Expert Join Date: Oct 2000 Location: SW Ohio Posts: 16,147	I thought my solution was less drastic Rat. __________________ "Leading the information hungry reefer down the road to starvation" Tom Current Tank Info: 130 Now out of service and a 29

01/26/2007, 02:47 PM	#3
MCary Premium Member Join Date: Dec 2002 Location: Hardin, Montana Posts: 3,142	That's a little high. I like to change my membrane if it goes over 10 ppm. Is your meter calibrated? What is the lower linear range of your meter? Mike

01/26/2007, 06:14 PM	#5
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	16 ppm is high for RO only even if your tap is only 143. Thats only 88% rejection. You want to be in the 96 to 99% range with RO only to maximize your DI resin life. A good rule of thumb is for every 2% you increase the RO membrane efficiency you double the life of the DI. Using a squeaky clean glass drinking water glass with no soap residue or water spots first test your tap water TDS, triple rinse the glass and meter in distilled or DI water, test your RO only without DI and again triple rinse both then finally test your RO/DI and rinse a last time then turn the glass upside down for clean storage and cap the meter probe. RO only should be 96 to 98% or more less than the tap water TDS so at 143 you should only be seeing 3 to 5 TDS. DI should easily be 0 indicated TDS. Prefilters and carbons have very little effect on TDS, they are there to capyure suspended solids not dissolved solids. Chances are you need a new RO membrane but do the testing first. It may only be worn out DI resin which when used up starts to release the contaminants it has captured back into the treated water. Never let DI get over maybe 2 or 3 or it will start to leach and possibly cause worse water conditions than waht your tap started out to begin with. Do not rely on color changing resin either as it is a really poor indicator. Always use a handheld TDS meter.

01/26/2007, 06:31 PM	#8
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	RandL524, I think the steps I have suggested will help you pinpoint your problem(s) before spending any money. If it turns out its only the DI cartridge thats great and less costly, but if you buy a new DI and it turns out the membrane is also bad and passing high TDS to the DI you will have worn out a new DI cartridge needlessly. Identify the problem first and it will probably cost you less in the long run. Without knowing what the RO only TDS is its impossible to know what to buy. Cross your fingers its only the DI and if you are really lucky your unit has a refillable DI cartridge and you can buy a bag of bulk resin and save even more money than having to buy a whole new cartridge.

01/26/2007, 06:35 PM	#9
WaterKeeper Bogus Information Expert Join Date: Oct 2000 Location: SW Ohio Posts: 16,147	I was kind of thinking that the 16 reading was off the DI stage but that may be wrong. Anyhow, I need to be nice to a guy from Connecticut even thought they deported me to Ohio three decades ago. __________________ "Leading the information hungry reefer down the road to starvation" Tom Current Tank Info: 130 Now out of service and a 29

01/26/2007, 08:08 PM	#10
drummereef Team RC Member Join Date: Jul 2006 Location: STL Posts: 14,754	If you are testing after the DI stage you need to replace the resin. You should be getting 0's after the DI. __________________ -Brett 180g Marineland Starfire In-Wall 278 gallon system

01/26/2007, 08:22 PM	#11
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	Again do not replace the resin without first testing the RO only TDS. If its bad and passing high TDS on to the DI you will waste a cartridge in a hurry. Yes you probably need new resin but why contaminate it if you do not need to? If your RO is bad you could be passing 143 ppm TDS to the DI and a brand spanking new 16 oz DI cartrdge would last about 14 gallons at that level.

01/27/2007, 04:08 PM	#12
randL524 Registered Member Join Date: Jan 2007 Location: CT Posts: 18	OK. My tap (using the triple rinsing clean glass technique - thank you Rat) was 126 ppm. the RO output (I revmoved the mxed-bed resin cartridge, rinsed the empty cartridge with distilled water and then let it fill) was 8 ppm, for a 94% RO efficiency. Not where it should be, but is it acceptable? Clearly the resin needs to be replaced. Do I spring for the $30 - $40 for a enw one, or can I refill the inner cartridge or recharge the resin...?

01/27/2007, 04:19 PM	#13
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	Looks like the membrane is still acceptable given your low tap water TDS. In my case with a tap TDS of over 800 I would go through resin like crazy with a 94% rejection membrane as it would be a TDS of about 50 going to the DI instead of my normal 7 or 8 from my 99.1% rejection rate membrane. You can see where a few % makes a big difference. If you have a vertical 10" canister type DI, I would get a refillable cartridge and a few bulk refills from one of the RC sponsors if the cartridge you have now is not refillable. It will probably cost you about the same as buying a throw away cartridge would locally. I think www.thefilterguys.biz had a good deal last time I was shopping for resin. You might also check www.buckeyefieldsupply.com and www.purelyh2o.com though and compare. Glad the membrane is OK as that will ave you some money for awhile longer anyway. Once the efficiency starts droping more though you might want to look into replacing it so DI will last longer, its a trade off, less money now on membrane but slightly decreased DI life or more money now on membrane and increased DI life.

01/27/2007, 04:23 PM	#14
WaterKeeper Bogus Information Expert Join Date: Oct 2000 Location: SW Ohio Posts: 16,147	I think why we disagreed slightly on this one Rat is you forgot that good old Dowex ion exchange resin tends to leach back ions when it become exhausted. This makes the TDS of the output of the train seem higher than the RO source water. __________________ "Leading the information hungry reefer down the road to starvation" Tom Current Tank Info: 130 Now out of service and a 29

01/27/2007, 04:49 PM	#15
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	I just didn't want to see him spend money on a new DI cartridge without first checking the membrane. That would be like throwing good money after bad since the resin would be exhausted quickly. I have seen this happen a few times and then they wonder why their DI only lasted 2 weeks. An RO/DI is a complete system and depends on every component to work effectively and cost efficiently. Poor or worn out prefilters and carbons shorten the life and decrease the efficiency of the membrane which in turn shortens the life and lower the effectiveness of the DI. It all has to work together! Thats like playing nice together as I tell the Grandkids.

01/27/2007, 05:26 PM	#16
WaterKeeper Bogus Information Expert Join Date: Oct 2000 Location: SW Ohio Posts: 16,147	Oh, and I agree. It's just that a spent DI showing 16 ppm is pretty common even with an RO stream down around 3-5 ppm. __________________ "Leading the information hungry reefer down the road to starvation" Tom Current Tank Info: 130 Now out of service and a 29

01/27/2007, 05:55 PM	#17
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	Absolutely, most people don't realize when a DI cartridge is exhausted it can quickly release contaminants at higher levels than are present even in the tap water. Once you start to see any elevated reading at all from the DI change it ASAP.