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inthesea
01/13/2011, 06:31 AM
I just hooked up a TDS meter to my RODI line. The reading from the tap water is 55 and the reading from the water the comes out of the RO membrane is 11 and the reading from the DI outlet is 0. I am wondering what should the reading from the RO membrane be and at what reading should it be changed?

James404
01/13/2011, 08:07 AM
This will depend on what RO membrane you are running, it sounds like your filters are fine though. Heres some good info from http://www.buckeyefieldsupply.com/FAQ.asp#FAQ7 on RODI filters.

When should I replace my filters?


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A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the useable life of these two filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. This is your indication one or both of the filters is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. The Matrikx+1 (“Chlorine Guzzler”) for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. Original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons.

Regarding your RO membrane and DI resin, use your TDS meter to measure, record, and track the TDS (expressed in parts per million) in three places:

1. Tap water
2. After the RO but before the DI
3. After the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 parts per million (ppm). Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block filter (collectively called “prefilters”) do very little to remove dissolved solids. So with your tap water at 400 ppm, you can measure the water at the “in” port on your RO housing and you'll see it is still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce less purified water (aka “permeate”), but have a higher rejection rate (96 to 98%). The life span of a RO membrane is dependant upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the total dissolved solids (TDS) in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce less water as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the 40 ppm water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm to 3 ppm, 5 ppm, and higher, you know that your resin needs to be replaced. Sometimes people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty” water. This will exhaust the resin quicker than would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!

Twichstile
01/13/2011, 08:33 AM
Your rejection is rate is a little low imo, I get 20-21ppm TDS post membrane before DI after filtering 380ppm tap. Your Membrane is at a 80% rejection which is very low but fortunately your tap numbers are not so high that you will exhaust DI resin prematurely.

My rejection rate is 95% and I have increased DI costs at the moment but I plan will replace my Membrane with a nice SpectraPure 98% rejection and upgrade to .5 sediment and .5 carbon to help protect the new membrane.

evsalty
01/13/2011, 08:47 AM
I just hooked up a TDS meter to my RODI line. The reading from the tap water is 55 and the reading from the water the comes out of the RO membrane is 11 and the reading from the DI outlet is 0. I am wondering what should the reading from the RO membrane be and at what reading should it be changed?
80% rejection rate is PATHETIC at best. If you had say 1000tds in and had 80% rej rate then maybe not so bad but to have only 55 in and yet still have 11 out something is wrong. This may not be the mambranes fault however. Rejection rate is greatly dependant on water pressure and also temperature. Do you know your water pressure going into your unit? Pressures less then 60psi will cause poopr rejection rates. Your pressure can also be affected by clogged prefilters. Now if pressure is at 60psi or higher then I would look into an exhausted mambrane. At that point get a Spectrapure mambrane. For your low tap tds I would not worry about getting the guarrenteed 98% membranes as all there mambranes are the same make. Spectrapure just tests each and every membrane and then selects the best of the best and then tests them even more so that they can feal comfortable putting the guarrenty on them.


Your rejection is rate is a little low imo, I get 20-21ppm TDS post membrane before DI after filtering 380ppm tap. Your Membrane is at a 80% rejection which is very low but fortunately your tap numbers are not so high that you will exhaust DI resin prematurely.

My rejection rate is 95% and I have increased DI costs at the moment but I plan will replace my Membrane with a nice SpectraPure 98% rejection and upgrade to .5 sediment and .5 carbon to help protect the new membrane.
You won't regret it.

My source is 450+ but I get 4-6 out of the membrane and it is well over 2 years old.

inthesea
01/13/2011, 09:08 AM
Thanks for the info, I don't have the pressure gauge installed. I know the membrane is pretty old (more than 3 years). Guess need to change out the membrane. You know I did not even realize I was running the ro unit without DI till couple days ago. I never had anyproblem with algae and all my corals have been doing good.

Twichstile
01/13/2011, 09:25 AM
Thanks for the info, I don't have the pressure gauge installed. I know the membrane is pretty old (more than 3 years). Guess need to change out the membrane. You know I did not even realize I was running the ro unit without DI till couple days ago. I never had anyproblem with algae and all my corals have been doing good.


Your situation is unique because you have such low tap tds.
Your corals are fine and you have no algae because you are still putting in 0 ppm TDS DI water ;)
Even though your membrane is in a horrible state of performance you are still only putting 11 TDS into your DI so even your DI will last a good while.

IF you change your membrane, you would definitely save DI costs. I would recommend getting Spectrapure filters and replace your 1 and 2 filters aswell but all that would probably cost $100 bucks..or you could just keep replacing your DI resin.

evsalty
01/13/2011, 10:10 AM
Here order from them off this link and it will be $55 + shipping to replace both the sediment and carbon block prefilters (see the kit price of $25 for the .5 micron ones) and the standard 90gpd membrane.

http://www.spectrapure.com/email/customer-appreciation.html

inthesea
01/13/2011, 10:46 AM
Thanks for the help, I'll check it out.

Buckeye Hydro
01/16/2011, 05:42 AM
Many times the real problem is the way in which the TDS is measured. Nearly any contamination in the sample container will cause an erroneous TDS measurement. Some plastic containers are difficult to get absolutely clean, and although they appear clean, they are not. An easy standard approach is to use a drinking glass as a sample container - use one right out of the dishwasher. Obviously, keep your fingers away from the inside surface of the glass.

Calibrate your meter. Use a calibration fluid generally in the range of the tds measurements you'll be taking. Some meters require a specific tds calibration fluid (e.g., 800 ppm), regardless of the tds levels in your samples.

Be careful with how you take your samples. Let's say you intend to measure the TDS in your 1) DI water, 2) RO water, and 3) tap water. Start with the cleanest of the three - the DI water. After letting the system run for a sufficient period of time that you are sure the tds levels have stabilized (to assure you are not measuring tds creep water), rinse the sample container two or three times with the water you intend to sample, and then fill the sample container with sufficient DI water to take a reading.

Now on to the RO water. The water we are interested in here is the permeate – i.e., the water that has been purified by the RO membrane – not the waste water. Make sure you understand which is which before taking the sample. Most RODI systems other than Buckeye Systems are not plumbed to facilitate taking a sample of the permeate. If that is the case, you’ll need to unhook some tubing – likely where the tubing attaches to the “in” port on the DI housing in order to take this sample. This is inconvenient for many people, and we find that people never do it. They report only the tap water TDS and the DI water TDS. Contact Buckeye if you need guidance regarding installing a couple of extra fittings and tubing to facilitate measuring the TDS of the RO water (permeate). When you take the sample, follow the same procedure described above – use a clean sample container, assure you are not measuring TDS creep water, rinse with the permeate several times before taking the sample, and use a calibrated meter.

Use the same approach to collect and measure your tap water as well.

Russ

GROSSR
01/30/2011, 01:45 PM
Can anyone answer this one, I change all 3 prefilter to the RO and now the output of the RO is HIGHER than the input?

I didn't flush the carbon block, also I have never calibrated my inline TDS meter due to the RO bringing it down to 2 or 3.

Now the input is 135 and the output is 188.

GROSSR
01/30/2011, 01:46 PM
Can anyone answer this one, I change all 3 prefilter to the RO and now the output of the RO is HIGHER than the input?

I didn't flush the carbon block, also I have never calibrated my inline TDS meter due to the RO bringing it down to 2 or 3.

Now the input is 135 and the output is 188. Input is before the system, output is after the Taste and odor cartridge.

Buckeye Hydro
01/30/2011, 03:55 PM
Check the alignment of the probes. You likely bumped them during installation... but I don't think it would make as much of a difference as your seeing.

GROSSR
01/30/2011, 07:55 PM
Probes have been there for 3 or 4 years with no issues. Just recently I changed the pre-filters. I have never seen the output of the RO higher than 8 or 10.

Buckeye Hydro
02/17/2011, 04:16 AM
If you still are struggling with this, feel free to give us a call when you are in front of the system and we can troubleshoot it with you.

Russ