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08/03/2009, 11:53 AM
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#1 |
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Registered Member
Join Date: Apr 2004
Location: Lake Crystal, MN
Posts: 654
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When to change RO Membrane?
At what point of TDS measurement do you change out your RO Membrane?
Thanks, Josh
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PBITAWA Current Tank Info: 150 Gallon Reef |
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08/03/2009, 12:13 PM
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#2 |
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Registered Member
Join Date: Mar 2009
Location: 45 mins from Chicago
Posts: 2,009
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You will find guys that say when it hits 10 they change it. Well I think that is a bit excessive. I change mine when it hits 30. I have been doing this because this is how my uncle taught me. He had successful reef tanks for 25 years. I have had mine over a year. Everyone has had an emergency here or their where they had to use Tap water....mine is 295tds. So if I am pushing RO at 20 tds thats well over 80% cleaner than my tap water....thats ok for a water change or two..........Also I do water changes every two weeks. If I do a change and my RO is close to 30 I will do another water change when I get my new filter.....not sure why but this is the way I do it and it works very well.....
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A wise man once said "Never play leap frog with a unicorn" Current Tank Info: 150 gallon glass with 20 gallon sump, 175lbs of coraline covered live rock, EuroReef skimmer rated for 250gal, 25watt Aqua UV sterilizer, Fluval FX5, Hamilton 3x250watt MH, 160 watt Blue actinic....Mixed reef |
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08/03/2009, 12:14 PM
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#3 |
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Registered Member
Join Date: Mar 2008
Location: Fayetteville, NC
Posts: 397
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wow- my well water is 54 out of the fixture- my spectrapure takes it to 00, but I have a TON of waste. Is there a way to maybe not purify it so much? LOL- but serious- I hate all that waste water...
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08/03/2009, 12:22 PM
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#4 |
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Registered Member
Join Date: Feb 2004
Location: Milwaukee
Posts: 6,081
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RO membranes are cheap, and for me at least, will keep TDS at 0 for a long time. So, I change them when I can no longer maintain 0 tds and I know it's not a result of my DI or other filters. There's little way to know what type of solids are getting through, so if you want to change it when you're at 10ppm TDS it could be pretty harmless stuff getting through or it could be something that is going to cause problems. Why risk it over $30?
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April 2015 TOTM |
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08/03/2009, 12:28 PM
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#5 |
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Registered Member
Join Date: Apr 2004
Location: Lake Crystal, MN
Posts: 654
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Where do you guys buy your Membrane?
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PBITAWA Current Tank Info: 150 Gallon Reef |
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08/03/2009, 01:03 PM
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#6 |
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Registered Member
Join Date: Jul 2004
Location: Chicago
Posts: 1,247
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What's your RO membrane rated for? Measure the TDS coming in and the TDS on the output with fresh prefilters. If you're not making its rated performance, time to replace.
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-Jim Current Tank Info: 70 gal custom room divider |
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08/03/2009, 01:37 PM
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#7 |
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Registered Member
 
Join Date: Feb 2004
Location: Carol Stream, IL
Posts: 23,162
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There is no set point when you should just the RO membrane. It is determined by the rejection rate, if the membrane is no longer producing water near -- or at -- its rejection rate it is time to replace it.
Couple of examples, RO membrane has a 96-98% rejection rate. Tap's TDS is 100, if the post RO membrane TDS is higher then 6 (( or so )) I would order a new one. RO membrane has a 90% rejection rate; Tap's TDS is 100, if the post RO membrane TDS is higher then 14 (( or so )) I would order a new one. Remember, the longer the RO membrane used after its rejection rate is used up the faster you will go through DI resin.
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Click my name and then "visit toddrtrex's homepage" for tank pictures Current Tank Info: 210g reef and 65g reef |
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08/04/2009, 01:20 PM
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#8 |
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RC Sponsor
 
Join Date: Jun 2003
Posts: 0
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Blitzburggirl:
What is your waste-to-product-ratio? If your tap water is that good, you can get away with an only 3:1 waste to product ratio. Call us about getting a "smaller" flow restrictor, or put a ball valve on the waste lline and dial it back to 3-to-1. Scott SpectraPure, Inc.
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Innovators in water technology. Since 1985! |
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08/04/2009, 02:32 PM
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#9 | |
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Meat Popsicle
Join Date: Jul 2007
Location: Portland, OR
Posts: 1,511
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Quote:
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-- He who learns must suffer, and, even in our sleep, pain that cannot forget falls drop by drop upon the heart, and in our own despair, against our will, comes wisdom to us by the awful grace of God. -- Aeschylus |
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08/04/2009, 03:52 PM
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#10 | |
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Registered Member
Join Date: Feb 2002
Location: Tennessee
Posts: 7,629
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Quote:
Because there are molecules that go through a RO membrane. Phosphate is a small molecule that will go through the RO membrane. That's why you need DI. While almost filtering the water may work for some, it's not best for everyone. So to the OP. To answer your question depends on how much DI resin you want to use up. If you don't like buying DI resin, replace the membrane when it gets to 96% efficiency. (Assuming you started with 98%) Tap in 300 out of RO 6 300 - 6 = 294 294 / 300 = .98 (good) ------------------------------------------------------------- Tap in 300 out of RO 10 300 - 10 = 290 290 / 300 = .96 Time to start shopping... |
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08/05/2009, 10:07 AM
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#11 |
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Registered Member
Join Date: May 2005
Location: Northern Virginia
Posts: 147
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What do you use to measure the TDS?
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08/05/2009, 10:23 AM
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#12 |
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Chalice Monger
Join Date: Jul 2006
Location: NW Indiana
Posts: 1,163
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i have a handheld meter that came with my ro/di from airwaterice
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08/07/2009, 03:08 PM
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#13 |
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Registered Member
Join Date: Apr 2004
Location: Lake Crystal, MN
Posts: 654
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I tested my input water and my cities water is horrible! It comes out around 700 TDS!!
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PBITAWA Current Tank Info: 150 Gallon Reef |
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08/11/2009, 02:22 PM
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#14 |
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RC Sponsor
Join Date: Jun 2003
Posts: 0
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Aquaman makes a good point regarding when to change membranes.
Let me give a supporting example- An average mixed bed DI cartidge should (many do not, but that is another story) process about 5000 ppm/gallons of ionic load. If all of your load is measurable as TDS on the meter you are using (note-you may have other issues like CO2 that present themselves as a ionic load as well, but it simplifies my example) then if your RO membrane is putting out 6 (the 98% rejection example that aquaman illustrated) then it would process about 5000/6 or about 833 gallons. If your membrane has gone down to 96%, then with 5000/12 or about 416 gallons (HALF the DI life). This is why a 4% loss of rejection performance is a big deal. Continuing this example, a 4% loss would be 5000/18 or about 278 gallons (a third of what you would get for lifetime if you had a 98% rejection membrane). Just imagine what happens if you have water like we do here in arizona (average TDS 800 to 1500 dpending on where you live). bruce bruce
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Innovators in water technology. Since 1985! |
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08/11/2009, 03:03 PM
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#15 |
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Registered Member
Join Date: Feb 2002
Location: Tennessee
Posts: 7,629
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Thanks for your insight Bruce. That is much better info than I had.
The rejection rate is why I railed against ebay RO units that were being sold with 90% efficient membranes. People were getting zero TDS out and thought that eveything was fine. But their DI was doing all the "heavy lifting". Some places have cleaned up their act but others have not. Just remember that zero TDS is not the Gold Standard of RO/DI. |
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08/11/2009, 03:35 PM
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#16 |
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Registered Member
Join Date: Apr 2004
Location: Lake Crystal, MN
Posts: 654
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Anyone ever run a dual membrane setup to lower the the TDS in areas such as Bruce and I's where the input TDS is in the high 600 or higher? Would this be beneficial or is it pretty pointless? Would I use less DI resin?
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PBITAWA Current Tank Info: 150 Gallon Reef |
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