RO membrane failure

[Tomoko Schum]

Hi y'all,

I just noticed that my RO membrane had failed and my TDS reading out of my DI cartridge is 97 ppm (vs. 134 ppm at tap) :eek2: I wonder how long it had been this way...

I am very surprised that my membrane failed so early this time. The previous one lasted a year at least and when I replaced it, I recall that it was reading still low teens.

It's a 100GPD Dow Filmtek membrane (supposedly a good brand) and I put this membrane into service at the beginning of January. When I changed my other filter cartridges and DI resin on 6/30/07, the membrane was still good.

Anyway, I have placed an order for the full set of filters and membrane again I also ordered a flush kit this time to extend my membrane life a little further. I am considering an in-line TDS meter that measures both my input and output TDS. I understand that a new Spectrapure has a nice one built in. H@rry's Spectrapure has a traffic light built in

I know that the life of RO membrane depends a lot on input water quality and sediment and carbon block filters must be changed rather frequently to protect the membrane.

How often are you guys changing these filters?

Tomoko

 

[kiran523]

My RO membrane on my unit is a GE Desal high rejection membrane (75 GPD). It's supposed to have a higher rejection rate (~97-98%) then the Filmtec but I haven't properly looked into it.

I was told that it needs to be replaced every 2-3 years. But like you said I'm sure it depends in the input TDS.

Melevsreef was saying that a flush kit and a 2nd DI membrane doesn't really make a difference but I would rather have one than not.

I ordered a set of sediment and carbon block from two part but I don't know anything about their performance. I'm sure Phillip could give us better advise on this matter.

 

[H@rry]

I can't remember exactly when I got my RO/DI unit but it was November of '99 or '00. I've never had to replace the membrane but I have replaced the filter cartridges many times. Like you said, I have a green light/red light test button to test my primary DI cartridge. When it tests red I move the secondary DI cartridge to the primary position and put a new one in the secondary. Also at the same time I can test my membrane by removing the DI cartridge, change a dip switch setting on the test unit, and pressing the button. It always tests good. I can't remember exactly how often I replace the sediment and carbon block cartridges but I think it's about once every 10 or 12 months (whenever I order new DI cartridges).

One thing that I have noticed it that some places sell 1 micron (or even 5 micron) sediment filters. Mine came with a .5 (that's point five) and the instructions cautioned against using anything larger leading to premature membrane failure. What are you using?

My sediment filter will change from solid white to solid rusty brown. I think you saw it and told me that was probably rust.

 

[Tomoko Schum]

Thanks, Kiran.

I heard that a flush kit does not do much before, but I thought, what the heck, it cannot hurt. I would like to get 2 to 3 years out of my RO membrane for sure. I forgot how many gallons that a membrane can treat. I produce about 20 gallons per week. 20 gallon x 36 to 37 weeks (Jan to Sep) means that this membrane produced less than 750 gallons.

As for the rejection rate, the rate of 75 GPD Dow Filmtek membrane is 96 to 98%. 100GPD is 90%. My previous RO membrane was GE's and the rejection rate was about the same if I am not mistaken. I use DI resin to bring the tds reading down to zero since tds reading of RO output usually ranges between 8 to 13 lately (it was as low as 3 a couple of years ago.)

Tomoko

 

[kiran523]

This is my setup:

Stage 1: 5 Micron Sediment
Stage 2: 1 micron carbon block
Stage 3: 0.6 micron carbon block
Stage 4: RO membrane
Stage 5 & 6: Refillable DI Chambers

Tomoko, what are you using for your 3 Stage carbon block?

 

[Tomoko Schum]

My 5 stage system is composed of a 100 GPD RO membrane with one 1-micron sediment filter, two 1-micron carbon blocks, and one 2.5x10 inch refillable DI unit.

As long as my tds reading out of my RODI system is zero, I am happy. I'd be happier if I could do this more inexpensively.

Spectrapure has 0.2 and 0.5 micron filters. Their 0.5 micron sediment (1) and carbon block filters (2) cost 2.5 times more than the set of 1 micron filters I bought from PurelyH2O.

If my membrane lasts 1 year, my total replacement cost (without DI) is $82 per year. Even if the 0.5 micron filter set can extend the life of my membrane 3 times, it's still cheaper to keep replacing the RO membrane + 1 micron filters every year. I think I just stick with my system and check TDS more often...

But I really want to know why my RO membrane had gone bad so eary this time so I can avoid that from happening again.

One thing PurelyH2O pointed out is that sometimes local water board may add something temporarily to remedy some problem such as a break in the system due to construction work. This can affect my membrane adversely. However, they said that there were so many factors that it was pretty difficult to pinpoint what caused my membrane to fail prematurely

Tomoko

 

[kiran523]

Very nice cost analysis Tomoko. Good info to think about.

 

[8BALL_99]

That sucks Tomoko, You already know what I do.. lol I just change them all when my TDS goes up in the Teens.. I get atleast a Year out of mine though.. If you change your prefilters out every 6 months or so like they say and you get 2 years out of your Membrane your really are no better off cost wise.. Same goes for the High end filters.. Sure they last longer but they cost so much more its a wash.. BTW if you got your unit from the same people I did just call them.. They will sell you a flush get at a discounted price.. I think I paid 15-20 bucks for mine.. They also sell inline TDS meters.

Will

 

[Tomoko Schum]

Thanks, guys.

I hope my experience will help some beginners out there - learning from other's mistakes/experience.

I change my prefilters every 6 months. If my prefilters extend the life of my membrane to 2 years, I save about $22 over 2 years by changing prefilters semi-annually as compared to changing out the whole set annually. However, it did not work out like that this time....

There might have been a manufacturing defect in this particular membrane to fail prematurely like this. I got a flush kit coming. I got my unit from the same people you got yours, but I have been buying my parts from PurelyH2O lately because of the better deal I get from PurelyH2O.

I just relocated my hand-held tds meter right next to my DI water outlet. You know, that extra few steps to fetch it sometimes keeps me from measuring tds. I am considering an in-line TDS meter (I am getting lazier and lazier...)

Tomoko

 

[bassetbros]

I have this TDS meter. I have one probe after my RO and one after my DI. That way I can tell what needs maintenance. On my Corallife Pure Flow II 24 gpd, my membrane lasted about 2 years producing <5 tds. I replaced it 2 months ago after recieving readings at or around 10 +. I change the sediment and carbon every few months when I notice the sediment prefilter becoming dirty.

God bless,
Basset

 

[bassetbros]

Oops...forgot the link:

http://www.tdsmeter.com/products/dualtdsmeter.html

 

[Tomoko Schum]

Thank you for the link. I will consider getting one in future. I just moved my tds meter right next to my di line so that I will pick it up as I connect/disconnect my water container to it. I will definitely be more diligent about checking.

I need to organize a group buy on 1 micron sediment and carbon block filters. I hate to pay so much shipping charge every time I place an order. We should be able to get a really good group discount from somewhere.

Tomoko

 

[NicoleC]

Formerly, I used a KDF prefilter on the house before it ever hit my RO, so my prefilters on the unit itself never got hammered at all. This thread reminds me that my prefilters are doing all the work now and I should probably change them soon.

My RO membranes (even with the old big setup and the baby fish) tend to last until I accidentally run hot water through, which I did once., It's a real "DOH!" moment.

 

[H@rry]

<a href=showthread.php?s=&postid=10784865#post10784865 target=_blank>Originally posted</a> by NicoleC
My RO membranes (even with the old big setup and the baby fish) tend to last until I accidentally run hot water through.

What is the longest that you know a membrane has lasted? Well, I guess that would depend on gallons and not the calendar. For a point of reference, I use about 42 gallons a week.

 

[NicoleC]

I don't really know. For me -- using a KDF filter but with LA atrocious water (tap TDS > 1000) -- lessee, I went two years changing about 15 gallons every week, plus the top off water at about 1 gallons per day, plus baby fish/cultures for about a year running about 5 gallons per day.

That's over 4000 gallons and still going strong. But the serious pre-filtration has to have helped.

 

[jrthomas40]

what kind of units are you all using???

 

[Tomoko Schum]

H@rry uses a unit from Spectrapure. Spectrapure RO membrane is considered the best in the industry according to an engineer that works for another RO membrane manufacturer.

Both 8Ball and I use 5 stage systems from an Ebay shop. I added a full size canister for DI resin to the original 5 stage system. Since I buy replacement filters and membranes from PurelyH2O and RO resins from 2partsolution, I am using the original system only as housing.

Tomoko

 

[8BALL_99]

Thats the thing.. Its a standard size.. Doesn't matter if you have a 99 dollar unit or a 400 dollar unit.. If it takes a 10" prefilter you can use any brand filter.. Same for RO membrane as long as you match the GPD You can use any of them.. If you want a Higher GPD Ro membrane all you have to do is change the flow restrictor out on the unit.. Its about a 10 dollar part..

 

[Tomoko Schum]

I got my prefilters, RO membrane and DI resin replaced and now my TDS reads zero at DI outlet, 10 at RO outlet. Tap water has 134 ppm.

When I checked the inside of first carbon block canister, the water in it was dirty. 1 micron sediment filter was not as red as the last two times (probably because it's less than 2 months since it was put into service.)

DI resin was orange on the top two third of the canister and still green in the bottom third, but its TDS reading was still 94 after all other components were changed, obviously releasing some trapped ion back into the water.

I am going to check my TDS at every water change until I get an in-line dual TDS meter. I will not buy another color changing resin - the color change part is really a waste of money. I thought it serves as a guideline, but the experience this time tells me "NO", it's not really reliable.

Tomoko

 

[8BALL_99]

I agree the Color changing resin is a waste..I ignore it and just go by what My TDS is after the DI

10 after your Ro isn't bad.. You would kind of think with only 134ppm for the input water it would be a little lower.. Its getting about time for me to be looking at new filters for my unit.. I'm not sure who I'm going to get them from..