HELP!!! I keep killing RO Membrane's

chrisguy · #1 09/06/2006, 10:35 PM

Background my tap water is about 120-130ppm. I flush the membrane every 2-3 weeks for about 1-2 minutes.

I bought my RO unit a little over a year ago. It's a 4 stage unit and was originally 50 gpd. After the first 6 months I replaced the sediment, carbon and DI. Shortly after that I found that I very quickly went through a DI cartridge, in about 1 month. In testing my water, the RO rejection had jumped from 2 - 4 ppm to about 25 - 30ppm.

So, under advice, I replaced the membrane with a 75 gpd and the flow restrictor. I could once again see a RO production water at 1-2ppm.

Low and behold a couple months ago I replaced the sediment, carbon and DI again and once again the RO rejection rate went up. This time I've tried to troubleshoot the issue to no avail. I did notice that the water pressure had dropped since the water company installed some a meter (was a little over 40psi before, dropped to a little over 30), so I purchased a booster pump. This added pressure, but I was still slowly eating DI cartridges. The RO production was back in the 20ppm range. The booster pump was installed post sediment and post carbon. I found conflicting information on if it should be pre or post carbon. Since the sediment and carbon were connected, I installed it post.

Tonight I removed the membrane to look for trouble, not that I knew what I was looking for. After putting it back in and flushing the membrane, the post RO membrane water is now 60 - 70ppm.

I did test the TDS meter and it is changing values and the in and out will read the same values when located pre or post DI.

I realize the RO membrane is once again bad and have ordered (again) a new one, this time a 100gpd with flow restrictor.

Can someone please tell me what the heck am I doing wrong?? I cant afford to replace EVERYTHING every 6 months.

Thanks in advance!!!!

BeanAnimal · #2 09/06/2006, 10:58 PM

Well we are missing a LOT of info.

What brand is the unit? Where did you buy the replacement parts? What brand membranes are you buying etc...

the 100 GPD membrane was not likely the best choice. At best it will habe a 90% rejection. That will give you somewhere between 10-13 PPM on the output side.

You want to use a DOWE FILMTECT 75 GPD membrane... not a GE DESAL, Applied Membranes, or DOW 100 GPD. The filmtec will give you around 98% rejection (2.6 TDS or so on the output) Thats a HUGE savings in DI resin.

Next you need to look at the seals and the pressure your pump is putting out.

In all honestly though... I would call any of the following reputable vendors for assistance. They will help you diagnose the problem and get it fixed with honest answers and no silly sales pitches or lies.

Bryan at Purleyh20.com
Walter at AirWaterIce
Buckeyfieldsupply.com
filterguys.biz

SkiFletch · #3 09/06/2006, 11:04 PM

I'll second the buckeye field supply reccomendation. They were a fantastic resource for me to get my original RO unit up and running. Great people over there. I wish I could help you out chris, but you've tried everything I thought of...

chrisguy · #4 09/06/2006, 11:23 PM

Sorry for the lack of details. When posting I didn't think the manufacture of the system was relevant.

What brand is the unit? It's from Aqua FX - 4 stage Barracuda
Where did you buy the replacement parts? Aqua FX ( www.aquariumwaterfilters.com )
What brand membranes are you buying etc... The current membrane is a 75 gpd filmtec. The replacement is 100gpd as that was listed on the site. I will call in the AM and try to change to a 75 GPD (or cancel the order and call one of the other vendors listed).

Next you need to look at the seals and the pressure your pump is putting out. No leaks as that would have been something obvious to troubleshoot and fix. The pump output pre RO Membrane is about 80 psi. I say about 80 because I also have a permeate pump so the pressure jumps to about 90psi with the pump.

As I originally stated, Thanks!! I will contact one of the above tomorrow and seek their advice.

AZDesertRat · #5 09/06/2006, 11:25 PM

Where are you buying the pre and carbon filters and what micron ratings are they? Is it a solid carbon block or GAC? What brand membranes were they and I second send the 100 GPD back and get a Dow Filmtec 75 GPD and nothing else, not an Applied nor a GE or especially any of the cheap e-bay knock off membranes.
Quality pre and carbon filters are what protects the membrane, try to skimp on price sacrifices quality which shortens the membrane life dramatically. I would also suggest getting a handheld TDS meter, the inline type is not very accurate as they are not truly temperature compensated, they read air temperature and how often are water temp and air temp the same?
What is your waste ratio and have you double checked it using a measuring cup or other device?

BeanAnimal · #6 09/06/2006, 11:37 PM

I would also add that 90 PSI is kinda pushing the envelope.... It is within spec, but if you don't have good seals on the membrane, then it may be bypassing in the housing.

chrisguy · #7 09/07/2006, 08:12 AM

The AM update. I got the order switched to a 75gpd membrane.

I am going to look into the local water reports. My thoughts are that there is a lot of chlorine in the water (I am guessing) and that the carbon is not holding up and killing the membrane. I have an extra canister so I am thinking that I should run dual carbon. Thoughts on this??

AZDesertRat · #8 09/07/2006, 09:18 AM

You don't have to run dual carbon but do use a high quality carbon block in a 1 or 0.5 micron size. They are good for 20,000 gallons of normal 1 ppm chlorine residual. Check your utility for chloramines that may also be a problem for you.

Thefilterguys · #9 09/09/2006, 12:07 AM

You have something going on but it's hard to say what. Your water report see link indicates chlorine as a disinfectant. If chlorine is destroying your membrane you have poor quality filters or a bypass somewhere.

http://www.grand-island.ny.us/news_i...news_index.htm

You should be fine with your booster pump Filmtec membranes can handle up to 300 psi and 80-90 psi with a booster is normal and not a problem.

Jim

BeanAnimal · #10 09/09/2006, 12:13 AM

I agree with JIM about the membranes and pressure... but would add that I have seen a lot of bypassing in the RO housing on "cheap" units and cheap membranes... thus my comments regarding 90 PSI. Personally I would love to have 90 PSI at the unit.. but I am to lazy to add a second pressure regulator to my main supply line.

Thefilterguys · #11 09/09/2006, 12:13 AM

I read back through your post and you say you have a permeate pump. Do you have a water tank on your system or did you mean you have a booster pump. Permeate require a tank to operate and generally do not provide high pressure.

Jim

Thefilterguys · #12 09/09/2006, 12:18 AM

One other thing it would be nice to know how much water are you making and any chance you have exposed your membrane to hot water?

Jim

chrisguy · #13 09/09/2006, 06:53 AM

Jim - Thanks for the great feedback. I did find and read that report. It just doesn't say how much chlorine is in the water. I am going to get a pool testing kit and test the water. I am also going to use it to monitor the water post carbon, to see if that is the issue.

For the other questions:

~ Yes I have a pressure tank.
~ No exposure to hot water.
~ I make about 30-35 gallons a week. That's usually about 20 gallons on Thursdays and 2-4 gallons every 2-3 days. My water is stored in a 40 gallon storage container.

dgasmd · #14 09/09/2006, 08:42 AM

How much water are you wasting or producing before your measuments? typically, you'll get much higher readins right after you turn on the water, but it should level out after about 3-4 g of production.
What is your product:waste ratio?

Just so you know, the prefilters should not be changed based in time, but rather based on how dirty your water is and how much water you use. At the volumes of water you are producing water and based on your starting TDS, your prefilters should last you well past 6 months. Also, I was given the advise of flushing the membrane for 1 minute every 6 hours the unit is working if at all possible for the best longevity. I suspect there is a mechanical issue with your unit and not a technical issue. Without looking at detailed pictures of your unit, it would be very hard to diagnose.

Hammercoral · #15 09/09/2006, 08:56 AM

Run more prefilters, my setup goes: micron filter, carbon, carbon, carbon, micron, RO, DI, and i change the carbon monthly they are only like $3 each makes the RO last much longer. Just get extra canisters at HD or Loes type places.

Thefilterguys · #16 09/09/2006, 10:02 AM

Chris for chlorine you municipal water system by EPA standards is required to not exceed 4ppm and generally you will see it in the 1-2 range. They can be off but they have to monitor and file a report.

A good chlorine guzzler carbon filter will handle any range from 1-4 like a snap good for 20,000 gallons of filtration. Since you are having troubles adding a second carbon filter would be a good choice but it still doesn't answer your membrane problem.

Jim

Thefilterguys · #17 09/09/2006, 10:29 AM

Lets talk about water testing when you fire up an RO system in the first minute you get a TDS burst which is very high. Then it settles down to nornal reading which in your case should be 2-4. Now if your system is turning and off all the time due to drinking water use your TDS will be high unless you have your drinking water isolated with a check valve. If it drains you water tank everytime you make DI water you tank will be very high in TDS causing your resin to exhaust fast. Any of this sound like it fits you? A Combined system has its pitfalls.

Jim

chrisguy · #18 09/09/2006, 10:45 AM

Not combined. My system is for aquarium use only.

Thefilterguys · #19 09/09/2006, 10:55 AM

I guess I'm confused do you have a permeate pump or a booster pump and what brand is it? Is the tank a storage tank or a pressure tank?

Jim

Unresistible Blue · #20 09/09/2006, 11:22 AM

Quote:

Originally posted by chrisguy
For the other questions:

~ Yes I have a pressure tank.

Does your system store DI water, or RO water in the pressure tank?

chrisguy · #21 09/09/2006, 11:43 AM

I have both a permeate pump (Aquatec 1000) and a pressure pump (Aquatec 8800). I started with the permeate pump but had to upgrade to a pressure pump when the town changed the meters and pressure dropped from ~45psi to just under 40psi.

My system stores DI water.

The storage tank has a float value used to shut off production. I was told this is functioning as a pressure tank.

I started the RO/DI unit today (on the old membrane) and after the initial production, the the TDS stabalized around 20ppm post membrane again. Not sure what happened that had it at 60-75ppm the other day. I am going to add a T and on/off pre DI and start sending the initial high TDS water down the drain, not through the DI as the initial TDS is 200+.

Thefilterguys · #22 09/09/2006, 12:57 PM

OK first of all you do not need both pumps if they are both connected drop the permeate off the system. What exactly is your storage tank?

With your tap TDS at 120-130 and a your old Filmtec 75 GPD membrane your post RO reading should be 2-4 so 20 is not right. An RO bypass will work for flushing that first burst which only lasts a minute or less.

Jim

Unresistible Blue · #23 09/10/2006, 04:53 AM

Quote:

Originally posted by chrisguy
My system stores DI water.

The storage tank has a float value used to shut off production. I was told this is functioning as a pressure tank.

The difference between your storage vessel and a pressure tank is that your vessel is not pressurized, and that it is presumably made of HDPE - so the DI water doesn't come into contact with the bladder within a pressurized tank - that's good.

There are a number of resons why you may have experienced that higher reading. For example:
You may have been testing the water immediately after turning the system on (the "tds creep issue.")
You could have been testing the tds in something other than a squeeky clean glass container
Your meter may have needed calibration

As was said above - if you have both pumps ditch the permeate pump.

With the high pressure provided by your 8800, and assuming you don't have unusually cold water, you should have post membrane numbers much better than 20.

Just so we make sure we have good readings, check the post-RO tds (pre-DI) again after letting the system run for 15 minutes. Use a newly calibrated tds meter and collect the sample water in a drinking glass right out of the dishwasher.

What is your waste : permeate (purified water) ratio?

Unresistible Blue · #24 09/10/2006, 05:01 AM

Quote:

Originally posted by Thefilterguys
An RO bypass will work for flushing that first burst which only lasts a minute or less.

Jim

I think Jim meant a "DI Bypass" rather than an "RO Bypass."