View Full Version : Membrane issue

09/26/2012, 10:34 PM
Hi Filter Guys,

Now that I know about your existence I regret a recent purchase I made. I will definitely be dealing with you Guys in the future.

I have an issue that I can't seem to figure out.

I purchased a Seachem Pinnacle+ from a fellow reefer about 9 months ago. He figured I would need new filters and membrane but he wasn't sure. He never really used the unit and didn't own a TDS meter. When I checked I was getting about 2-3 TDS after the DI and figured I could run with that.

Everything was good until recently. The TDS was creeping up even after a few pre-filter changes so I decided to get a new membrane.

I got a Dow Filmtec 75gpd and corresponding restrictor and I have run hours worth of water through it and the lowest reading I can get before the DI is 25! That is down from 60!

My question is, did I get a lemon? Ripped off on the Internet? My psi is about 75. I'm at a loss. Do you have any advice? Thank you, sorry so long winded.

Erik Stevenson

10/01/2012, 08:45 PM
Erik sorry for the delay we have been at MACNA in Dallas. What is the tds of your tap water?

I almost always expect a 97-98% rejection rate from Filmtecs. What replacement restrictor did you get?

I have more questions but lets start from here and this will eliminate usless questions on my part.


10/01/2012, 08:59 PM
Thank you for responding, no problem waiting, I figured you must have been busy with something. I hope MACNA was a blast. I hope to go sometime in the future.

My tap is in the 390's, after the prefilters is about 250, and the restrictor is a 550. But I have been using my old 800 restrictor because with the 550 my pressure was up around 90 psi. My pump has no adjustment feature.

Thanks again for any help

10/02/2012, 03:42 PM
Just off the cuff you may want to try reinserting your membrane and not forcing it all the way in but use the screwing of the cap to drive the membrane into place. Some membrane housings ave very technical about positioning to prevent water bypass. Once you have reseated your membrane you may need to do several 10-15 minute flushes to free up the membrane. This is done by removing the flow restrictor or using you flush valve if you have one, look to see if your RO tds is dropping. Get the 550 restrictor back on as the 800 is for a 100 gpd and not helping, and 90 psi is good operating pressure. Hopefully you have good quality carbon filters, ours are made for pressures up to 150 psi. Let me know if your seeing improvement or we can change something.


10/04/2012, 10:20 PM
Well, I've tried what you suggested. I really appreciate you taking the time to help me with this.

So far, my best result is still around 25 TDS coming out of the permeate side of the membrane. I have wasted a lot of water in the last ten days trying to get this to come down. I'm really stumped.
My DI knocks it down below 10 but I'm afraid it's going to be exhausted soon. By the way, my pump is online after my carbon block so no worries about pressure on that.

Thanks again

10/04/2012, 10:48 PM
Your only getting 95% from your Filmtec membrane and I always expect better but with your high tds you may have impacted your performance when the rejection rate was even poorer @60. I don't know what else to suggest for better performance at this stage.

Now another matter with your DI, we always expect zero tds with a new cartridge and consider them exhausted at a reading of no higher then 2-3.


10/05/2012, 08:19 AM
Just a note, I suspect the membrane issue has something to do with the style of membrane housing Seachem is using as this is not the first time this has come up. We get our hands on membranes like your now and then and are able to free them up to 97-98% rejection by flushing. It tells us the issue is either the housing along with high tds or incorrect membrane placement that is the issue. however when large volumes of water have been passed through the membranes they are harder to recover.

Membranes cost a lot of money so most people just ride out the less then expected performance because it can't be corrected.


10/05/2012, 10:51 AM
Yes, I suspect the housing as well. I have gone back to the old membrane for the time being. I guess I'll have to eat this mistake. I learned to stick with the 100gpd membranes at least with this system. Thanks for all your help, I will be looking you guys up very soon for a new membrane.

10/05/2012, 01:20 PM
I don't think it is the membrane GPD but the membrane housing that may be the issue. Was the 100 GPD a Filmtec membrane?


10/05/2012, 01:35 PM
It's the original membrane, I think it says DCM 100. I'm not at home right now so I can't check. I do know that both seem to seat in the housing well, but the diameter of the new one is at least 1/4" smaller,which I would expect, but the outer gasket seems to seal like it should.

10/06/2012, 08:12 PM
Interesting about the size and I think you have just come up with the SeaChem issue. Membranes and housings are usually standard size. The Seachem membrane appears not to be standard and if it is oversized the housing may not be standard either. This could create a slight water bypass issue with a Filmtec membrane.

We have always wondered why they built with 100 GPD membranes as they lack performance with only a 90% rejection rate. When a produce is not standard it lacks flexability.


10/06/2012, 11:00 PM