Most reliable RO membranes

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vikubz

New member
The last RO membrane I bought doesn't seem to be working too well.

I measured my tap water at 229 ppm, and 91 ppm after the membrane. It was new in September, and I didn't notice anything until I got a color change DI add-on. The resin seemed to be depleting too fast, so I got a TDS meter and found the readings above.

I tried reseating the membrane to see if maybe it wasn't installed properly, but that didn't help.

Besides temp and pressure, what are some other factors I should look at before declaring this a case of a bad membrane?
Are Dow Filmtec membranes considered a good brand?


Thanks!
 
dow is the BEST
then there are many lesser brands ending with the ones who dont even label

and yes there is a difference.
i use 2 dows at work along with 1 no name. the no name gets about 90 percent rejection and hte older dows still are getting about 95 percent.
 
The membrane I have now is a 50 gpd dow which I got from purelyh2o.

I'm thinking I'll just have to order another one.
 
Wait before even considering putting another membrane in there, I would try to determine why you membrane only lasted 8 months. My first membrane went 4 years and I only replaced it because I wanted to upgrade it. I would not put a $100 spectraselect membrane in there until you get things solved first. Do you change out your carbon filters regularly? I would get a chlorine/chloramine test kit and measure your waste water to see if you are getting break through. My guess is that something is wrong if your membranes are only lasting 8 months. Do you believe this membrane was functioning properly when you first got it or do you think it was defective from the start?
 
I know my first membrane was damaged because of tap water that was too hot. We had a faulty valve in an upstairs shower which was sending hot water back down the cold pipes.

After this was fixed I got a new membrane. Unfortunately I did not have a TDS at the time and assumed the membrane was fine, only realizing it wasn't when the DI resin seemed to be going awful fast.

Would chloramine in the waste indicate that there's a breach in the membrane?
 
Could be the membrane isn't seated right. Those things have to go in and be pushed in pretty hard to get past the double o-ring on the end. Might want to take it apart and just re-seat it first to see if that makes a difference. Also, good to take it apart to see what it looks like. I have seen some that have a black coat around them. They really shouldn't look too different from the day you put it in - just a little darker in color perhaps.

I second the stay away from the 100 GPD membrane. Those do not have as high of a rejection rate as a 75 GPD membrane.

If you do have chloramines in your tap water you may require a special type of carbon to remove it. I had a friend with this problem. Can't remember the type of carbon though.
 
<a href=showthread.php?s=&postid=9634709#post9634709 target=_blank>Originally posted</a> by vikubz
I know my first membrane was damaged because of tap water that was too hot. We had a faulty valve in an upstairs shower which was sending hot water back down the cold pipes.

After this was fixed I got a new membrane. Unfortunately I did not have a TDS at the time and assumed the membrane was fine, only realizing it wasn't when the DI resin seemed to be going awful fast.

Would chloramine in the waste indicate that there's a breach in the membrane?
Click to expand...
TFC membranes (Filmtec from Dow) are very sensitive to chlorine which can damage the membrane very fast. If your carbon filter was not replaced on time and you had chlorine or chloramine passing to the membrane that can shorten its life considerable. If you detect any chlorine (or chloramine) before or after the membrane that is most probably the cause.
If not, also try testing your waste to product ratio. If the ratio is too low (lower tha 4:1 the mambrane gets incrusted and pluged by calcium deposits.
 
<a href=showthread.php?s=&postid=9634709#post9634709 target=_blank>Originally posted</a> by vikubz
Would chloramine in the waste indicate that there's a breach in the membrane?
Click to expand...

The reason I suggest testing for chlorine in the waste water line is because it is the easiest place to access. The waste water has gone through the prefilters, including the carbon block, and therefore should be chlorine free. If it is not, then that will be an issue. I also agree with testing the waste to pure water ratio. I would perform some of these simple tests before putting another membrane in there.
 
If chlorine has made it to the waste line its too late.
Lots of vendors especially the e-bay variety use low quality carbon filters, some of them still use granular carbon which has a very low chlorine and VOC capacity so it gets exhausted very quickly, sometimes in as little as 200 or 300 gallons of normally chlorinated tap water. Good quality solid carbon blocks on the other hand can go as long as 20,000 gallons.
The membrane is only one component in what should be what is considered a filtration system or unit. It takes every component in that system to operate efficiently and last for any length of time. Cheap prefilters cause carbons to fail prematurely, just like cheap carbons cause membranes to fail and cheap membranes cause DI to fail. It pays to buy the best components and use them as a package for the best water quality and unit life. Thats why units like the Spectrapure MaxCap are so successful, they use all the best pieces and they work well together making each one of them last and last thus saving you money in the long run.
 
That is a very good filter you should have had no problem with chlorine. You can find chlorine tablet kits from pool supply stores.
 
What is your waste water to permeate ratio? That will help determine if you are getting any bypass flow in the RO membrane housing.

Russ @ BFS
 
Tonight I'm going to take the unit apart again and see if there's any problem with how it's seated in the housing. I don't think there is, but I'll take a look.

What's the best way to determine the waste/product ratio? Run a known amount of RO and see how much waste water you get?

Here is a link to a report on our local water. Does anything stand out that could be a problem?

http://www.cfu.net/pdf/water_report.pdf?loc=top
 
Take two buckets and have the product water run into one and the waste water into the other enough to collect about two cups of product. Then use a measuring cup to measure the amount of each.
Normal ratio is 4:1 or 5:1

There is nothing in the report the unit should not be able to take care of.
 
Well, I checked the waste to product ratio, and it's right at 4:1, so I guess it's not a problem of bypassing the membrane.

Perhaps I just got a bum membrane. I contacted purelyh2o, so maybe there's a warranty solution.
 
I have a 3 year old Dow Filmtec 75 gpd membrane right now. I just took measurements tonight.

Tap Water = 580 ppm TDS
RO = 8.4 ppm TDS
RO/DI = 0.6 ppm TDS

I am getting a 98.55 % rejection from a 3 year old membrane. I think the Filmtec 75 gpd is the 2nd best choice to a Spectrapure Select. I got lucky with this membrane. Not bad for a $40 membrane. All of my measurements came from a Com-100 meter.

Later
Drew
 
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