Brand new RO Membrane reading really high TDS, is this normal?

Hey Guys!

So I’ve just got this RO membrane, it’s a Dow Filmtec XLE-4040 Extra Low Energy Commercial RO Membrane. I got it from Amazon but it’s also sold on the website, so I’m pretty sure it works fine for this. Anyways, I’m here in Las Vegas, and the TDS is about 750 PPM. After hooking up the Filter, the TDS Meter is still reading about 740 PPM. I’m curious, does this every happen with a brand new RO Membrane?? After I flush it, will it go down to what it’s supposed to, or is this just a bad membrane??

Thanks in advance guys!!

1 Like

well i’m not an expert but when i replaced my axeon input was around 180 output started higher but went down to about 3. there is a thread where i give the detail.
700+ is very high and would expect output of around 35
here is the post i made that details time and results New R/O membrane today

Now when you say that the output started higher, exactly how high?? Like was it the same as the input, at 180??

You didn’t mention your other filters, you’re not running that straight off of the tap are you? Please say you got some prefilters on it…

What was your pressure? any drop on the backside, or output?

Are you letting your brine out? (wastewater)

A little bit more on your setup would really help.

Thats a pimp of a filter, was looking at those myself. It’ll last you a long time. What size did you get, its the four footer right? Yellow one?

Your tds ain’t nothing compared to here for sure, and your RO should bring it down to zero. If it ain’t, you’re gonna need DI tanks.
If you run your set up like the following, you will keep your DI for about a year or longer if you have a cubic foot of mixed bed resin, personally I don’t have an RO setup but run a pretty well built DI system that saves me a ton of money on DI.

Get yourself 4 big blue housings, and you can get a triple housing mount for cheap if you look around, but in those filters, one will be your sediment filter, try for hi flow at 5 mic’s or less. The other 3 will be hi flow coconut carbon filters. Don’t fall for the “activated” garbage. It’s all activated. Coconut carbon is the best and lasts longest, go for the 4 inchers because the 2 inchers are next to impossible to fit right into the housing.

Price will depend on monsoon season, and hurricane season in the islands where they harvest the coconuts. Bulk is the best deal.

So, run from tap to a pressure regulator (so you can tie in to a water main or a backflow with high pressure preferrably one with 600 pounds down to zero. Get the kind that don’t have reject valves on it.

From regulator to sediment filter, to carbon, to carbon, to carbon, to bypass…one to your RO, the other to booster pump then to RO.

From RO to bypass, one to your DI, one to your supply hose.
From your DI to your supply hose.


Hey thanks for the reply!

So I have a Carbon Pre-Filter to filter out the chlorine, than I run into the RO Membrane. After that I have it running into the Unger nLite HydroPower Stage 1 Unit. If I’m not mistaken, yes, the brine is being let out on the bottom of the unit there’s a 1/2 inch outlet where water is coming out of, which I believe is the brine…Do you think that the PPM will read high just for now, but than eventually go down substantially. Because right now it’s basically reading the same PPM out as the PPM in…

the waste eater has to be regulated/adjusted but i don’t know how, the wash it (now xero pure) has some kind of automatic adjustment others have taps.

That question is out of my realm of expertise, I’m sorry. I have never even seen one of those units. I don’t know if it’s an RO unit as well or just DI. As for the RO membrane you bought, my advice is to check the specs on the unit. Its a commercial unit, which is not what WE understand as commercial-you probably already know that though-but some of those units are meant for extremely high pressure and/or for SPECIFIC pressures that maybe you’re not hitting.

Doesn’t Dow Corning make those? If I were you I would call them, they are a really good company that absolutely stands behind their stuff, I’m positive they can walk you thru it if its the membrane.

Because, the Unger unit you have should already be taking down the TDS, if you’re getting the same as tap, then there’s obviously a problem with both. I’m assuming the Unger unit is DI only?? If so, if it’s new, call Alex (he’s a member and product specialist here on the forum and at the store) and he will absolutely get to the issue on the Unger unit and sell you new resin if thats the issue. I’d call him when he has a good ten minutes to talk to you tho, so when you get hold of him ask him if its a good time to talk (he’ll always say yes so you kinda gotta listen to the tone of his voice-he’ll probably make time for you anyway but just so he ain’t rushed its best to ask)

He’s a good dude and will help you if he can.

Sounds like you already know what you are doing, so I can’t call it. If the brine is let out (have you played with the flow?) then the membrane should be doing its job unless the pressure is off (not correct) and its not able to do its job? Thats all I can think of. Sorry I couldn’t help you more than that.

1 Like

again you can’t just let the brine pour out it must be regulated. have you read the instructions? or asked the supplier?

… I’d be interested to hear about your setup as I run DI only as well and
would like to know how to reduce resin usage. My tds here is way lower than
yours too 150-400.

1 Like

i run ro only most of the time 150-200 tds input

With a RO unit each membrane has a specific calculated ratio. This ratio is for the pure water verses the waste water. With the Xero pure there is a preset valve on the housing that controls the high and low side of the RO membrane. You need to make sure your waste valve setting for the Dow membrane is set proper. Did you get the housing and membrane at the same time? Are they both from Dow? You may need to contact them to get the proper configuration.


I’m gonna call them right now to see if I can figure this out. Thanks

Is this in a DIY system?

Yeah it is, can you help with this??

Sounds like you have the plumbing wrong.

Post some photos

1 Like

Tap to pressure regulator.
Regulator to sediment
sediment to carbon, carbon, carbon,
to DI (2 tanks with 1.5 cubic feet)
to another sediment filter at 10 mics
I have pressure gauges at every connection
I have one bypass after the DI to inject acid in the hoses to clean them and flush after a year or so.
I have a lab quality tds meter at the end of the system and a cheapo tds meter just after that to keep it honest.

What saves the DI is the carbon blocks. Sometimes you’ll have to tap into reclaimed water which is really high in chlorine and will be the death of your resin in a heartbeat if you have that in your state/city.

Also, the DI tanks I use (rentals) are meant for an optimal pressure of 80-85psi. That’s NOT for the fiberglass tank itself but for the resin to do its job. It has a tendancy to start making channels inside the tank at lower pressures, where not all of the resin is making contact with the water as it should. So keeping it at that PSI, FOR ME AND MY SYSTEM, keeps my tanks fresh.

Here’s a picture of what I’ve got going on. Sorry it’s in Landscape, my phone is messed up and I can’t take pictures in Portrait. Anyways, basically its tap to Carbon Filter, Carbon to RO Membrane, RO Membrane to DI Unit.

Do you have 3 connections on the RO?

Inlet (from carbon)
Concentrate (waste water/bypass)
Permeate (good water - to DI)

I only see 2.

There is no connection for the waste water. It comes out the bottom. I need a connection??

Where can I get a flow restrictor for this size Membrane??