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Old 05-25-2007, 02:31 PM   #1
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nitrates in rodi water

Hi, quick ? My rodi water has high nitrates(40-same as the tap) I am going to replace the prefilters and it is close to time to replace the di so I'll do that too. Will this work for the nitrates or do I need to replace the membrane too? I just ask because if so I need to order the membrane but I have the others on hand.

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Old 05-25-2007, 04:27 PM   #2
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Sounds like your membrane is bad, and once that happened it quickly depleted your DI. If it was just the DI that was bad, you should be seeing at least some decrease in nitrate readings between the tap and the unit's outlet - but you aren't.

Are you testing for nitrates using a test kit, or do you mean a TDS reading of 40ppm? If using a test kit, I'd first make sure that your test kit isn't bad. If you have access to a TDS meter, you might use that to get a feel for what exactly is being removed, and at what stage.
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Old 05-25-2007, 05:41 PM   #3
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thanks
I do mean Nitrates with a test kit. I test every week for Nitrates, Ca, Alk. I skipped testing nitrates just 1 week so I have done 2 water changes and the usual 1-2gal top off each day for 2 weeks since testing. The tank has been at 0 for 4-5 months and when I tested and it was about 10 I knew something was wrong. So I tested the batch of sw I have premixed- almost 40 then I tested the barrel of rodi for my top off controller-40.
I was just thinking about ordering a tds tester a few days ago cause I realized it was past time to replace the prefilters(something like 8 months and I use a moderate amount of water). I got a set of prefilters and a di cart. when I got tthe unit.
Anyway I was just wondering if the membrane is what takes the nitrates out.
Can anyone recommend a good place to buy a membrane for a standard 10" ro unit??
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Old 06-11-2007, 08:45 AM   #4
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Hi everyone. I got it fixed. There was nothing wrong with the membrane I just replaced the sediment filter, the carbon filters, and the DI and now there is no Nitrates and a TDS reading of 1.
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Old 06-11-2007, 09:17 AM   #5
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So be careful who you listen to because I rushed to order a membrane and as it turns out there is nothing wrong with the one I have.
That is just plain rude. The folks here do their best to help others. Frankly, I would have told you to replace the membrane as well. Please be a little more appreciative of the help you are given and if not appreciative then civilized.
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Old 06-11-2007, 11:10 AM   #6
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Sorry didn't mean that like it came out. I should have done more research before buying the membrane. from what I understand the prefilters really do a lot of the work of taking stuff out the water and the membrane sort of polishes it off. And whatever else the DI does it also takes the TDS on mine down to close to zero from 235 coming out of the RO unit.
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Old 06-11-2007, 12:02 PM   #7
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Quote:
Originally Posted by Hara
Quote:
So be careful who you listen to because I rushed to order a membrane and as it turns out there is nothing wrong with the one I have.
That is just plain rude. The folks here do their best to help others. Frankly, I would have told you to replace the membrane as well. Please be a little more appreciative of the help you are given and if not appreciative then civilized.
I'll try not to respond in kind, but if you replaced the DI cartridge it's a pretty much no brainer that your TDS will be 0. You can trickle very high TDS water through ONLY a DI cartridge and get 0 ppm... for a brief while.

I'll put big money up that you'll be back here in less than a month wondering why your TDS and nitrate readings are back high again. It's because you blew through your DI resin with high TDS water. Your RO membrane does more than "polish" the water. If you've got a TDS of 235 coming out of your membrane, you have problems with your membrane. But don't take my word for it - why don't you contact the folks you bought it from! Much more information there than a bunch of dumb folks on this here internet thing.
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Old 06-11-2007, 01:43 PM   #8
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But don't take my word for it - why don't you contact the folks you bought it from! Much more information there than a bunch of dumb folks on this here internet thing.
Good advice, before I posted the ? in the first place I did contact the person I bought it from: http://www.melevsreef.com/ro_di.html
And while I was waiting for his response I thought I'd ask you guys.
And his advice was DO NOT REPLACE THE MEMBRANE- IT IS GOOD FOR 2-3 YEARS. I have only had it 8 months.
If you look back I deleted what I said.
And I said I was sorry
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Old 06-11-2007, 07:54 PM   #9
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If you have 235 coming out of your membrane then its shot.. They do make bad membranes. The prefilters do some work, its the membrane that does most of the work. Your TDS out of the membrane should be 30 or under depending what your tap TDS is.
Good luck.. And keep a eye on the nitrates. I have a feeling your DI will get used quickly with a TDS of 235 going through it.
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Old 06-11-2007, 08:06 PM   #10
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The TDS coming out of the membrane will depend on the membrane and the incoming TDS. The water pressure and temp would play a part too. Most membranes have a 96-98% rejection rate. Most 100 gpd membranes have a 90% rejection rate.

It would mean your incoming TDS is really bad though. With a TDS like that after your RO, your DI won't last long.
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