RO Membrane Quality Declining?

[H@rry]

Over the past couple of months I replaced my RO membranes due to high TDS in the output. My tap is about 95 - 115 TDS and after new membranes is has always gone down to about 3 TDS (I have 2 membranes). When it gets to anything over 6 TDS I replace the membranes and that corrects the issue. Several months or so ago I replaced the membranes but still got high TDS with new membranes. I wondered if there was an issue with the membrane housings as they were over 20 years old so I replaced them with new ones, still no help.

A week ago I replaced the membranes with Dow FilmTec 75 GPD (American Made), ran the "break-in" 3 gallons of output to the washing machine. Now a week later and probably less than 200 gallons I have 4 and 10 TDS after the new membranes. Could I be getting defective membranes?

 

[Red_Beard]

You changing the carbon filters out too? Chlorine/ Chloramine eats membranes and tds will climb fast like that.

 

[Kmst80]

You changing the carbon filters out too? Chlorine/ Chloramine eats membranes and tds will climb fast like that.

My thought, should change sediment and carbon filters first, a membrane should last 2+ years if you keep your other filters up to date.

 

[H@rry]

Sediment and Carbon filters were changed 90 days ago. I change them every 6 months.

 

[Doctorgori]

That seems pretty frequent
Are you regularly back flushing your membranes?
I had over 500ppm tap and my RO membrane lasted over 1yr …
what brand/source are you using?
hmmmm

 

[KStatefan]

Sediment and Carbon filters were changed 90 days ago. I change them every 6 months.

Does your water supply contain chlormines? How many gallons is your carbon filter rated for? It is possible that 6 months is to long depending on what you have.

 

[H@rry]

I'm using Dow FilmTec 75 gpd.

This never has been an issue with the carbon blocks (I have two of them) but I'll order some more membranes and carbon blocks this time and see if that helps.

 

[Red_Beard]

The only other thing to check, would be the housing, make sure it isn't cracked or scored down in the bottom where those double o rings seat between effluent and permeate lines. or if there isn't something like a burr that would score the o rings to prevent a proper seal.

But, having experienced what you are experiencing currently, i have found that the most likely culprit is chlorine getting past your carbon blocks and deteriorating the membrane. I now always change all prefilters if i do the membrane, and if not, i rotate them through about every 6 months.

 

[Malcontent]

There are counterfeit Dow membranes out there.

Mine seem to last forever whether I'm on ground water or surface water or have chlorine or chloramine.

I'm getting 0.02 mg/L chloramine after 4 (out of 5) carbon stages. Once it ticks up to 0.03 mg/L it's time to rotate in some new carbon. Some places can have more than 2X the chloramine that I do so...