Issues with newer Dow filmtec 75 gpd RO membranes?

[t5Nitro]

Anyone having issues with recent membranes from Dow not lasting very long?

I put two membranes in not too many months back and have usually pre-DI TDS of 4-5. Today, the pre-DI TDS after the membranes reads 10.

I imagine this is an issue with the RO membranes and not as much an issue with the prefilters? The prefilters and both membranes I changed prior to making maybe upwards of 300 gallons of product water.

My RODI unit has the following order:
Sediment > carbon > carbon > chloramine monster > RO mebrane 1 > RO membrane 2 > mixed DI resin

I have the unit running through an RO buddy booster pump. I forget the microns of the prefilters. I believe they're 5 micron sediment, 5 and 1 micron carbons.

 

[blaxsun]

My base TDS is around 210, something like 30 after the sediment and carbon, 1 after the membrane and 0 after reain.

 

[t5Nitro]

Alright, I've not tested after the pre filters, but sounds like the membranes need replaced already then. Looked back to see when I got them. May last year. Didnt last long!

 

[Blue Spot Octopus]

I thought you put the chloramine monster first and then into the system?

 

[NormanB]

Do you backwash the membrane pre and post usage?

 

[Blue Spot Octopus]

Sorry ignore

 

[t5Nitro]

Do you backwash the membrane pre and post usage?

What is this? I run waste water until pre TDS goes to the usual place post membrane before I valve it open to the DI before production.

 

[t5Nitro]

I thought you put the chloramine monster first and then into the system?

Chloramine monster should be incorporated after the prefilters IMO, then you've exposed source water to cheap prefilters and carbon blocks before hitting the costly chloramine monster filter.

 

[Blue Spot Octopus]

Ok thanks

 

[t5Nitro]

Just as follow-up, check your post-membrane TDS if using these filters and burning through DI a bit quicker. My post membrane measured 10 and reduced to 3 after changing them. The membranes seemed to have exhausted a lot sooner than usual. Maybe the filmtec brand had a bad batch. Hopefully the new ones last longer than 10 months (and I don't do water changes so my use has mostly been for top off purposes).

 

[Opus]

My base TDS is around 210, something like 30 after the sediment and carbon, 1 after the membrane and 0 after reain.

I would love to know what is in your water that the carbon block is taking out. Normally you will only see a 1 or 2 tds drop or increase after the prefilters.

 

[Opus]

What is this? I run waste water until pre TDS goes to the usual place post membrane before I valve it open to the DI before production.

You are doing it correctly. Some RO dealers push the flushing of the membrane between uses to prolong the life but there is no evidence that this actually does anything but waste water.

 

[blaxsun]

I would love to know what is in your water that the carbon block is taking out. Normally you will only see a 1 or 2 tds drop or increase after the prefilters.

It's probably not the carbon but the sediment filter that's pulling the bulk of it out (I'm only measuring before the pre filters and after the membrane and resin).

 

[Opus]

It's probably not the carbon but the sediment filter that's pulling the bulk of it out (I'm only measuring before the pre filters and after the membrane and resin).

The sediment filter only takes out suspended solids, it isn't small enough to remove dissolved solids, unless you have one with some ridiculous small micron size. Mine is .2 micron and it doesn't do anything to tds.

 

[blaxsun]

The sediment filter only takes out suspended solids, it isn't small enough to remove dissolved solids, unless you have one with some ridiculous small micron size. Mine is .2 micron and it doesn't do anything to tds.

All I know is my TDS is around 210 going in and around 30 going into the membrane/resin (I was able to measure this when flushing the system for a new membrane and resin filter).

 

[spsick]

Exposure to chlorine (or chloramine) and not sufficiently flushing carbon both foul membranes quickly. I rinse my carbon blocks really well and still found the last membrane I replaced was a little black.

Other thing is when running 2 membranes the second one will foul much quicker than the first due to the higher TDS reject water feeding it.

 

[Opus]

Exposure to chlorine (or chloramine) and not sufficiently flushing carbon both foul membranes quickly. I rinse my carbon blocks really well and still found the last membrane I replaced was a little black.

Other thing is when running 2 membranes the second one will foul much quicker than the first due to the higher TDS reject water feeding it.

I'm not sure not flushing the carbon filter will foul the membrane "quickly", at least not in my experience. I've been using RO units since the mid 90's and up until the last couple of years I never flushed my new prefilters and I still got 5+ years out of my membranes.

Also, he has 2 carbon blocks plus a chloramine monster filter before his membranes so I doubt chlorine is the issue. I guess it could be if they did some kind of maintenance on the water system and drastically increased the chlorine. I know I recently got an email from my water district that for several weeks in March they would suspend using chloramines and go to strictly chlorine as a sanitizing measure.

 

[t5Nitro]

I don't rinse my new carbon blocks either. I haven't had issues before from that. After the unit has been running a bit longer, it went from TDS pre-DI 3 and post-DI 0 to now pre 1 and post 0. I think that's the best I've ever had it. I'm still going with a bad batch of membranes on the previous purchase.

 

[jimk60]

Where did you purchase your filmtec? Dow has had a problem with cheap nock offs for awhile. They actually have an app that will scan your filter to verify that it's genuine. Check the Dow website.

 

[t5Nitro]

My new ones are certified. Post-membrane x2 TDS had been 3 when new. Filled a 65 gallon tub a few times and now it's back to the same thing as follows. I'm wondering if anyone is having this issue and has a solution?

Turn on the RO system, waste the first bit of water to get the TDS down to 4-5, then switch it over to the DI and get post resin TDS of 0 to the storage tank.

However, under an hour of running, the post-membrane TDS went from 5 to 7. I anticipate that as I keep it running, the post-membrane TDS will go back towards 10. Seems like the rejection rate is high. The membranes can't be exhausted already?