RO/DI flow restrictor question

[Tom@HaslettMI]

I just looked at the membrane in my RO/DI unit and realized it is a 100 GPD membrane (Filmtec TW30-1812-100). I got this unit used about a year ago and have had TDS reading in the 14 - 18 range from day one. I was never too concerned since the RO water I was purchasing from the local grocery store had similar readings. However, I'm now ready to get down to 0 TDS.

I think the root of the TDS problem may be the flow restrictor... I replaced the old one prior to running the unit with a 50 GPD model (the quick connect type) because that was what was on the unit and I made the assumption that it had a 60 GPD membrane (it is a 60 GPD spectrapure unit).

So, my questions are as follows:
1) Would a 50 GPD restrictor on a 100 GPD membrane be why I am getting TDS above 0?
2) Is the current membrane shot due to the mismatched flow restrictor?
3) Is a spectrapure 90 GPD capillary restrictor appropriate even thought the membrane is 100 GPD?
4) Can someone point me to the thread @AZDesertRat posted about how to install a capillary flow restrictor?

Thanks for the help,
Tom

[BeakerBob]

Tom, I can't answer all your questions, but can point you to some good info:

1) Sizing Flow Restrictors

2) Reef Thread

3) BuckEye Supply

I have been using SpectraPure products fro a couple years now and find they they have lasted much longer then the other manufacturer/vendor product that UI was using before.

[AZDesertRat]

The 100 GPD Dow Filmtec is the worst possible choice for a membrane, it is not even a Reverse Osmosis (RO) membrane but is in fact an Nano Filter (NF) membrane. The difference is the RO is a 96-98% rejection rate or removal efficiency device intended for 3 log removal of viruses, bacteria and oocysts in drinking water while the NF is only a 90% rejection rate device intended for "Pool and Spa Use" as designated by the ANSI/NSF and is not approved for drinking water use in the USA.

Your TDS problem is the poor membrane more than anything. You will never see low TDS out of that NF membrane, it was not designed to do so.

The 90 GPD Spectrapure membranes start out life as a Dow Filmtec 75 GPD RO membrane rated at 96-98% rejection rate then Spectrapure treats them with a special proprietary process proven to increase the GPD and rejection rate then they subject them to testing, either batch testing in the case of their normal series or for $10 more you can get the individually hand tested and guaranteed in writing to be better than 98% rejection Select series membrane for only $45. A matched capillary tube flow restrictor is $5.

I use the Select series myself, my RO/DI is 5 years old and the membrane is still producing water at 99.4% rejection rate or removal efficiency today. The savings in DI has been tremendous.

When you figure that for every 2% you increase the rejection rate, you double the life of your DI resin I have save countless DI replacements over the past 5 years, actually its been 10 years as I sold my old Typhoon III at that time and bought my first MaxCap then but have since upgraded to the UHE system 5 years ago. Its money in the bank.

What is your tap water TDS, RO only TDS and final RO/DI TDS? What is your water temperature and water pressure? Do you use softened water or do you know the hardness of your water? Have you measured your exact waste ratio and if so what is it? These are all question that need to be answered to troubleshoot a RO/DI system.

Are you using Spectrapure replacement sediment and carbon block filters? Are you using Spectraure SilicaBuster DI replacement resin or cartridges? Is your DI resin fresh and if you buy in bulk is it stored in a vacuum sealed bag in the back of the refrigerator so it stays damp and out of direct lighting? Resin has a fairly short shelf life especially once it has been opened, bulk resin often is not the answer as it lloses its cationic and anionic properties when it dries out.

[Tom@HaslettMI]

Thanks for the links Bob.

AZ I appreciate all of the info. I guess I'm going to be getting a new membrane and flow restrictor, which answers my first three questions.

Here are my TDS numbers ect.

Tap: 235
RO: 16
DI: 16
Temp.: 60 F
Pressure: 50-55 PSi
Softener: Not used
Hardness: 3 dKH tested with TropicMarin kit (seems low?)
Waste ratio: never tested
Sediment filter: Spectrapure 0.5 micron
Carbon block: Spectrapure 0.5 micron
DI resin: unknown. The stuff that was in the unit is still in there. When I initially started using it it was probably already shot, and I figured replacing it when the output still had TDS was unwise. Honestly, I'm not sure I want/need to run DI resin... what are your thoughts?

Please let me know if you need additional information.

Thanks for your help,
Tom

[AZDesertRat]

You are at 93% rejection rate. you want to be at 98% or better.
Your DI is definitely shot so is nothing more than a wide spot in the pipe at this point.
I would always use DI, there are things that RO bys itself are not particularly good at removing like silicates, nitrates and phosphates among others. Its cheap insurance.

With a new membrane such as Spectrapures hand tested Select series you should be able to get your RO only TDS down to 2 or 3 or less but DI is still worth the $18-$25 or so and it will last almost forever. My Phoenix tap TDS is 630, my Select membrane gets that to between 2 and 3 TDS using a handheld COM-100 TDS meter and my DI lasts over 1000 gallons per cartridge.

You need to know your waste ratio also, when you buy a new Spectrapure membrane they suggest you get a new capillary tube flow restrictor which comes with directions on how to calculate your waste ratio and trim the capillary tube for your exact measured conditions. I check mine every so often to make sure things are not changing.

Something interesting I forgot to mention is, for every 2% you increase your RO rejection rate, you double the life of your DI resin. Imagine how long DI will last if you improve your rejection frpom 93% to 99+%, thats a 6% improvement which means the DI will last probably up to 7x longer than without the changes. More than pays for a RO membrane every several years in DI savings alone.

[Tom@HaslettMI]

Good info thanks.

I pretty much knew all along that the DI was shot. I am planning to get the 90 GPD select membrane and matching flow restrictor. But I would appreciate a recommendation for the type of DI resin... there are a ton of options on the Spectrapure site.

Thanks,
Tom

[Tom@HaslettMI]

Also what are your thoughts on Matrix USA 0.6 micron carbon filter? The reason I ask is I'm planning to order a few things from Premium Aquatics and they have all of the SpetraPure items I want except the carbon filter and DI resin. Your thoughts on the DI resin they have would also be appreciated.

Thanks so much,
Tom

[AZDesertRat]

If you have a single DI, the SilicaBuster or better yet Super SilicaBuster would be my choice. If you have dual DI canisters than I would go with the MaxCap/Super MaxCap in the first position and SilicaBuster/SupersilicaBuster in the second. My current MaxCap and SilicaBuster cartridges are still plugging away at 0 TDS, believe it or not they were installed as replacements on 10/10/2011, I just checked my logbook, but will try the Super versions next replacement. I can't believe its been 16 months with zero replacements and still working.

The Matrikx +1 0.6 micron is a good carbon block. Don't know how prices compare, I think Spectrapure gets like $12 or $13 for their 0.5 version.