tds meter readings?

dzeadow · 01/07/2008, 10:52 AM

ok, so I have a V series RO/DI from PurelyH2O which has one of those cheap replaceable DI chambers that sits horizontal vs. vertical. Well, I'm going to replace this w/ a vertical one but I have a question about the TDS readings I'm getting so I know whether or not I need to swap the RO membrane or filter cartridges at all. I got one of those free TDS meters from buy.com when there was a huge rush of those a little ways back so I know that it's probably not completely accurate, but here's what I read, 122 tap/waste, 13/14 before DI, and 7 after. Is it ok to just get the new DI cannister so I can get it to 0? or does it look like I need other new filter cartridges? TIA

kwjones · 01/07/2008, 11:02 AM

Replace the other filter cartridges as suggested by the manufacturer. Personaly...I went 2 years before replacing anything in my RO/DI and then just replaced everything at once.

If you're getting 13-14 ppm out of the RO filter, I would replace the RO membrane. My tap water is 120ppm, after the RO membrane it's down to 1-2ppm and 0 after the DI filter.

dzeadow · 01/07/2008, 11:16 AM

hmm.. I've only had the unit since Sept., so I'd assume that most of the filters are probably ok. sounds like I need a new RO membrane and will get better performance from the vertical DI as well.

kwjones · 01/07/2008, 11:38 AM

Just another aside...

I have a handheld TDS meter and just installed a dual inline TDS meter. The handheld meter said my final product was 25ppm while the inline showed 0ppm. It could be that the container I was using for the handeld wasn't entirely clean and threw off the reading. So it may have to do with how you're testing the water.

I like the dual inline meter before and after the DI filter because it lets me guage when it's time to replace the RO membrane or when it's time to replace the DI resin.

AZDesertRat · 01/07/2008, 12:00 PM

Inline meters should be used as a rough guide only. They are not temperature compensated so are not accurate unless your water and air temperature are exactly the same.
Lets look at how you are using your handheld meter.
First, get yourself a clear drinking water glass, make sure it is absolutely squeaky clean, no water spots and especially no soap residue. I hand wash my glass in hot water, not the dishwasher.
Next, draw a sample of tap water in the glass, stick the meter in and let it stabilize. Record that reading. Now very important, triple rinse both the glass and the meter in DI or distilled water. Always do this between tests and when done so both stay squeaky clean!
Now draw a sample or RO only water before DI. Again stick the meter in and let it stabilize and record the reading. As before triple rinse the glass and meter.
Finally take a sample of the RO/DI and drop the meter in. Record that final reading and triple rinse the glass and meter, cap the meter and turn the glass upside down to keep dust and salt spray out so it is ready for next time.

Now look at your readings. The RO only TDS should ideally be 96-98% less than the tap water TDS. Using you numbers from before, if tap is 122 then your RO only should be between 3 and 5 TDS. If your waste is still 13-14 then you are getting less than 90% rejection or efficiency. You do not have the 100 GPD membrane I hope ???? If you do then you are in the ballpark but if you have the much more efficient 75 GPD then you are not doing so well.

DI should be 0 or very close to it. If its anything other than 0 TDS, I change my DI.

I would stick with the handheld and a clean glass as it is far superior to the inlines available today.

dzeadow · 01/07/2008, 12:19 PM

The V series from PurelyH20 is the 75gph version. I did not test as you have stated which could be a problem. I used a brand new disposable plastic cup and didn't rinse between readings. If my ro/di water isn't as pure as 0, is rinsing it w/ the ro/di water going to give me false readings as well, like I should go get some wallyworld distilled to rinse with? I'm glad I'm getting this info. I have tested the water out of the ro/di before for phosphates and didn't get a reading, but if I'm still getting high tds readings, it's probably not helping my hair algae situation any is it?

AZDesertRat · 01/07/2008, 02:06 PM

Once DI resin nears exhaustion it begins to release weakly ionized substances. A few of these include nitrates, phosphates and silicates. Since they are weakly ionized to begin with they may not register well on some TDS meters either so what appears to be 0 TDS RO/DI water may not in fact be 0.
Something to keep in mind is a good rule of that that says, "For every 2% you increase the RO membrane efficiency, you double the life of the DI resin". So you want to keep the membrane as efficient as possible for maximum DI life and efficiency. Refills can soon add up in cost and that's the big difference between a good unit and a so so unit, the one may cost more initially but it will save you money in refills from day one.

01/07/2008, 10:52 AM	#1
dzeadow Premium Member Join Date: Sep 2007 Location: Bozeman, MT Posts: 2,589	tds meter readings? ok, so I have a V series RO/DI from PurelyH2O which has one of those cheap replaceable DI chambers that sits horizontal vs. vertical. Well, I'm going to replace this w/ a vertical one but I have a question about the TDS readings I'm getting so I know whether or not I need to swap the RO membrane or filter cartridges at all. I got one of those free TDS meters from buy.com when there was a huge rush of those a little ways back so I know that it's probably not completely accurate, but here's what I read, 122 tap/waste, 13/14 before DI, and 7 after. Is it ok to just get the new DI cannister so I can get it to 0? or does it look like I need other new filter cartridges? TIA __________________ - Danny Current Tank Info: Dual 50 Breeder system, 30g custom sump/fuge, MSX200, Tank1-6x24T5 retro, Tank2-4x39T5 retro

01/07/2008, 11:02 AM	#2
kwjones Registered Member Join Date: May 2003 Location: Rising Sun, MD Posts: 373	Replace the other filter cartridges as suggested by the manufacturer. Personaly...I went 2 years before replacing anything in my RO/DI and then just replaced everything at once. If you're getting 13-14 ppm out of the RO filter, I would replace the RO membrane. My tap water is 120ppm, after the RO membrane it's down to 1-2ppm and 0 after the DI filter. __________________ Honorable Golden Shellback "Lemon Curry????"

01/07/2008, 11:16 AM	#3
dzeadow Premium Member Join Date: Sep 2007 Location: Bozeman, MT Posts: 2,589	hmm.. I've only had the unit since Sept., so I'd assume that most of the filters are probably ok. sounds like I need a new RO membrane and will get better performance from the vertical DI as well. __________________ - Danny Current Tank Info: Dual 50 Breeder system, 30g custom sump/fuge, MSX200, Tank1-6x24T5 retro, Tank2-4x39T5 retro

01/07/2008, 11:38 AM	#4
kwjones Registered Member Join Date: May 2003 Location: Rising Sun, MD Posts: 373	Just another aside... I have a handheld TDS meter and just installed a dual inline TDS meter. The handheld meter said my final product was 25ppm while the inline showed 0ppm. It could be that the container I was using for the handeld wasn't entirely clean and threw off the reading. So it may have to do with how you're testing the water. I like the dual inline meter before and after the DI filter because it lets me guage when it's time to replace the RO membrane or when it's time to replace the DI resin. __________________ Honorable Golden Shellback "Lemon Curry????"

01/07/2008, 12:19 PM	#6
dzeadow Premium Member Join Date: Sep 2007 Location: Bozeman, MT Posts: 2,589	The V series from PurelyH20 is the 75gph version. I did not test as you have stated which could be a problem. I used a brand new disposable plastic cup and didn't rinse between readings. If my ro/di water isn't as pure as 0, is rinsing it w/ the ro/di water going to give me false readings as well, like I should go get some wallyworld distilled to rinse with? I'm glad I'm getting this info. I have tested the water out of the ro/di before for phosphates and didn't get a reading, but if I'm still getting high tds readings, it's probably not helping my hair algae situation any is it? __________________ - Danny Current Tank Info: Dual 50 Breeder system, 30g custom sump/fuge, MSX200, Tank1-6x24T5 retro, Tank2-4x39T5 retro

01/07/2008, 12:00 PM	#5
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	Inline meters should be used as a rough guide only. They are not temperature compensated so are not accurate unless your water and air temperature are exactly the same. Lets look at how you are using your handheld meter. First, get yourself a clear drinking water glass, make sure it is absolutely squeaky clean, no water spots and especially no soap residue. I hand wash my glass in hot water, not the dishwasher. Next, draw a sample of tap water in the glass, stick the meter in and let it stabilize. Record that reading. Now very important, triple rinse both the glass and the meter in DI or distilled water. Always do this between tests and when done so both stay squeaky clean! Now draw a sample or RO only water before DI. Again stick the meter in and let it stabilize and record the reading. As before triple rinse the glass and meter. Finally take a sample of the RO/DI and drop the meter in. Record that final reading and triple rinse the glass and meter, cap the meter and turn the glass upside down to keep dust and salt spray out so it is ready for next time. Now look at your readings. The RO only TDS should ideally be 96-98% less than the tap water TDS. Using you numbers from before, if tap is 122 then your RO only should be between 3 and 5 TDS. If your waste is still 13-14 then you are getting less than 90% rejection or efficiency. You do not have the 100 GPD membrane I hope ???? If you do then you are in the ballpark but if you have the much more efficient 75 GPD then you are not doing so well. DI should be 0 or very close to it. If its anything other than 0 TDS, I change my DI. I would stick with the handheld and a clean glass as it is far superior to the inlines available today.

01/07/2008, 02:06 PM	#7
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	Once DI resin nears exhaustion it begins to release weakly ionized substances. A few of these include nitrates, phosphates and silicates. Since they are weakly ionized to begin with they may not register well on some TDS meters either so what appears to be 0 TDS RO/DI water may not in fact be 0. Something to keep in mind is a good rule of that that says, "For every 2% you increase the RO membrane efficiency, you double the life of the DI resin". So you want to keep the membrane as efficient as possible for maximum DI life and efficiency. Refills can soon add up in cost and that's the big difference between a good unit and a so so unit, the one may cost more initially but it will save you money in refills from day one.