RO/DI TDS Reading - Its this normal?

ddgluck · 07/28/2007, 02:46 PM

Just wanting some feedback on my ro/di reading ...is this normal?

My tank is doing fine, just having some algae in the water column issues as of late. I do all the regular water changes, maintenance.. .etc..

Details -
3 month(500 gallons)old - 6 stage purewaterclubDOTcom RO/DI 100GPD

Tap Water = 185ppm -- I thought this was pretty good
Pure Water = 14ppm
RO water - before DI and Carbon = 18
Waste water = 205 - can my waste water be higher than my tap water?

All TDS readings were taken with a new calibrated TDS meter.

Let me know what you think, or if you have any feedback.

d4a2n0k · 07/28/2007, 04:47 PM

Your input water is 185ppm and after the RO you get 18ppm which is about a 92% rejection rate. Truthfully, thats not that good.

You dont have a true RO membrane, rather an RO filter. You are eating up the DI resin very quick using something with a 92% rejection rate. If you were using a Dow Filmtec membrane, your RO water would be about 4ppm instead of 18ppm. A true RO membrane should get about a 98% rejection rate. For every 2% you add on the rejection rate, you double the life of the DI resin.

Your water should read 0 after the DI, especially with such low TDS on your tap water. It sounds like your DI resin is shot and needs replacement. You should look into getting a Dow Filmtec RO membrane because it will make your DI resin last 6 times as long as it does now.

frank2926 · 07/28/2007, 05:01 PM

your filter is ok . Its just you could have made a better selection when You picked your filter. A 100gpd filter should only give you a 90 percent rejection rate. Yes you are going thru more di than you would with a better membrane. Yes your waste water should be higher. You just took say all of the contaminates in 4 gallons of water and added them to your waste say 3 gallons of water. remember all the bad is going out in your waste. And with a final product number of 14 I would say your DI is exhausted. Time for a refill or replacement.

ddgluck · 07/28/2007, 06:26 PM

Yea - that's what I was afraid of.... crappy filter.

I'm going to order the 75gpd FILMTEC RO MEMBRANE from The Filter Guys, along with some new DI Resin.

Thanks for all the GREAT replies.

-dg

d4a2n0k · 07/28/2007, 06:38 PM

Make sure you get the proper flow restrictor as well as you will be stepping down the GPD.

The initial cost of the Filtec membranes is hard to swallow but as long as you keep up with replacing the prefilters, it should give you 3-5 years of service. It will also pay for itself eventually as you wont be replacing the DI resin as much.

07/28/2007, 02:46 PM	#1
ddgluck Registered Member Join Date: Jun 2005 Location: St. Louis Posts: 79	RO/DI TDS Reading - Its this normal? Just wanting some feedback on my ro/di reading ...is this normal? My tank is doing fine, just having some algae in the water column issues as of late. I do all the regular water changes, maintenance.. .etc.. Details - 3 month(500 gallons)old - 6 stage purewaterclubDOTcom RO/DI 100GPD Tap Water = 185ppm -- I thought this was pretty good Pure Water = 14ppm RO water - before DI and Carbon = 18 Waste water = 205 - can my waste water be higher than my tap water? All TDS readings were taken with a new calibrated TDS meter. Let me know what you think, or if you have any feedback.

07/28/2007, 04:47 PM	#2
d4a2n0k Registered Member Join Date: Oct 2003 Location: Long Island, NY Posts: 2,485	Your input water is 185ppm and after the RO you get 18ppm which is about a 92% rejection rate. Truthfully, thats not that good. You dont have a true RO membrane, rather an RO filter. You are eating up the DI resin very quick using something with a 92% rejection rate. If you were using a Dow Filmtec membrane, your RO water would be about 4ppm instead of 18ppm. A true RO membrane should get about a 98% rejection rate. For every 2% you add on the rejection rate, you double the life of the DI resin. Your water should read 0 after the DI, especially with such low TDS on your tap water. It sounds like your DI resin is shot and needs replacement. You should look into getting a Dow Filmtec RO membrane because it will make your DI resin last 6 times as long as it does now.

07/28/2007, 05:01 PM	#3
frank2926 Registered Member Join Date: Feb 2003 Location: phila Posts: 1,645	your filter is ok . Its just you could have made a better selection when You picked your filter. A 100gpd filter should only give you a 90 percent rejection rate. Yes you are going thru more di than you would with a better membrane. Yes your waste water should be higher. You just took say all of the contaminates in 4 gallons of water and added them to your waste say 3 gallons of water. remember all the bad is going out in your waste. And with a final product number of 14 I would say your DI is exhausted. Time for a refill or replacement.

07/28/2007, 06:26 PM	#4
ddgluck Registered Member Join Date: Jun 2005 Location: St. Louis Posts: 79	Yea - that's what I was afraid of.... crappy filter. I'm going to order the 75gpd FILMTEC RO MEMBRANE from The Filter Guys, along with some new DI Resin. Thanks for all the GREAT replies. -dg

07/28/2007, 06:38 PM	#5
d4a2n0k Registered Member Join Date: Oct 2003 Location: Long Island, NY Posts: 2,485	Make sure you get the proper flow restrictor as well as you will be stepping down the GPD. The initial cost of the Filtec membranes is hard to swallow but as long as you keep up with replacing the prefilters, it should give you 3-5 years of service. It will also pay for itself eventually as you wont be replacing the DI resin as much.