when to change RO membrane

[reefin101]

My ro/di unit is almost 2 yrs old now. It is a BRS 5 stage dual DI unit. I have probably processed about 12-15k gallons thru it. Anyway, it seemed when new that the TDS coming out of the membrane was about 1-2ppm......
I am now seeing about 4-5ppm and I do have newer prefilters that I changed out about 1800g ago. I have changed along the way, just stating that these are fairly new and shouldnt be increasing the TDS.....

Anyway is it about time for a new membrane since the TDS have crept up?

Oh I do have a membrane flush and that has been done recently as well and still getting 4-5ppm TDS after membrane,

 

[shecter]

its probly time. i have the brs 5 stage plus and new im getting 0 tds. seems like something is off. i wish i could help more but id say replace it.

 

[wysiwyg]

it is definately time to change the membrane

 

[Buckeye Field Supply]

This is our most frequently asked question. From our FAQ's list:

A good rule ofthumb is to replace your sediment filter and carbon block after six months. Amore precise way to maximize the usable life of these two filters is to use apressure gauge to identify when pressure reaching the membrane starts todecline. This is your indication one or both of the filters is beginning toclog.

Also be cognizant of the chlorinecapacity of the carbon block. A good 0.5 micron carbon block for example willremove 99% of the chlorine from 20,000 gallons of tap water presented at 1 gpm.Some original equipment suppliers commonly provide carbon cartridges rated at2,000 to 6,000 gallons. Remember that all the water you process, both wastewater and purified water, go through the carbon block.

Regarding your RO membrane and DIresin, use your total dissolved solids (TDS) meter to measure, record, andtrack the TDS (expressed in parts per million [ppm]) in three places: 1) tapwater, 2) after the RO but before the DI, and 3) after the DI.

The TDS in your tap water will likelyrange from about 50 ppm to upwards of 1000 ppm. Common readings are 100 to 400ppm. So for sake of discussion, let's say your tap water reads 400 ppm. Thatmeans that for every million parts of water, you have 400 parts of dissolvedsolids. How do we go about getting that TDS reading down to somewhere nearzero?

If you do some experimenting withyour TDS meter, you'll note that your sediment filter and carbon block (collectivelycalled “prefilters†because the treat the water before it reaches the membrane)do very little to remove dissolved solids. So with your tap water at 400 ppm,you can measure the water at the “in†port on your RO housing and you'll see itis still approximately 400 ppm.

The RO membrane is really theworkhorse of the system. It removes most of the TDS, some membranes to agreater extent than others. For instance, 100 gpd Filmtec membranes have arejection rate of 90% (i.e., they reject 90% of the dissolved solids in the feedwater). So the purified water coming from your 100 gpd membrane would be about40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce purifiedwater (a.k.a. “permeateâ€) more slowly, but have a higher rejection rate (96 to 98%).The lifespan of a RO membrane is dependent upon how much water you run throughit, and how dirty the water is. Membranes can function well for a year, twoyears, or more. To test the membrane, measure the TDS in the water coming in tothe membrane, and in the purified water (permeate) produced by the membrane.Compare that to the membrane’s advertised rejection rate, and to the samereading you recorded when the membrane was new. Membranes also commonly producepurified water more slowly as their function declines.

After the RO membrane, water willflow to your DI housing. DI resin in good condition will reduce the TDS in theRO water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1ppm, you know that your resin needs to be replaced. Sometimes people complainthat their DI resin didn't last very long. Often the culprit is amalfunctioning RO membrane sending the DI resin “dirty†water. This willexhaust the resin quicker than would otherwise have been the case. Sometimesthe problem is poor quality resin – remember that all resins are not createdequal.

Additionally, don’t forget tosanitize the entire system at least once per year, and wash and lube yourhousing o-rings with food-grade silicone grease every filter change.

Russ

 

[reefin101]

its probly time. i have the brs 5 stage plus and new im getting 0 tds. seems like something is off. i wish i could help more but id say replace it.

You are getting 0 TDS after your membrane! Wow either you have the PIMP membrane or you have very clean water coming into your house...

it is definately time to change the membrane

Why? I don't prefer to spend money just because it seems like i have processed "alot"of water or the filter is "old" etc.....

This is our most frequently asked question. From our FAQ's list:

Russ

Thanks for the info, but i am not sure I read when to replace the membrane. I thought somewhere inthe past i heard read that when the output of the membrane starts to rise a few ppm over it's new output it is time to replace?

So i think I m there but just cheking.

 

[Buckeye Field Supply]

If a membrane has gone bad you'll typically see one of two things:
1. The rejection rate goes down
2. Production slows. But cold temperatures and low water pressure also slow production. You can use the calculator on our home page to see how fast your membrane should be producing water given your temperature and pressure.

Russ

 

[MBG75]

Russ gave you all the info needed.

To make it easier.

What is your Tds before the membrane?

What is your Tds after the membrane?

What is your Tds after the DI

 

[solitude127]

Russ gave you all the info needed.

To make it easier.

What is your Tds before the membrane?

What is your Tds after the membrane?

What is your Tds after the DI

Just a quick question, why is TDS after the DI important when we're talking about the membrane?

 

[Bubbles_B]

great information. not many people have asked this question. glad that members of the R2R community have chimed in.

 

[MBG75]

Just a quick question, why is TDS after the DI important when we're talking about the membrane?

To see if the DI is exhausted

 

[Flipside]

It really is a great idea to buy a non-portable TDS meter, and strategically place it in your RO/DI's runs. I have a 2 port one that measures my tap water, and after the RO membrane. I plan on labeling a safe range on the RO membrane (with a P-Touch labeler, or Sharpie, or something), so I will know when it's starts to foul on me.

You can see my setup here: https://www.reef2reef.com/forums/member-tanks/95516-flips-reef-4.html if you're interested. Getting good readings from my new filters, FWIW! Big shout out to Russ/BFS for teaching me all this jazz, back in the day!

 

[reefin101]

If a membrane has gone bad you'll typically see one of two things:
1. The rejection rate goes down
2. Production slows. But cold temperatures and low water pressure also slow production. You can use the calculator on our home page to see how fast your membrane should be producing water given your temperature and pressure.

Russ

goes up is subjective. can you quantify. Goes up by 1ppm or 10ppm or 2% or 5%, etc....

Russ gave you all the info needed.

To make it easier.

What is your Tds before the membrane?

What is your Tds after the membrane?

What is your Tds after the DI

before 175
after 4-5
after DI 0

Just a quick question, why is TDS after the DI important when we're talking about the membrane?

ditto,

To see if the DI is exhausted

i know when it is exhasuted, anything other than 0

 

[MBG75]

before 175
after 4-5
after DI 0

Ok. So if you have 175 TDS in, then

If its a 90% rejection membrane. Max allow out is 17.5 TDS

If its a 96% rejection membrane. Max allow out is 7 TDS

If its a 98% rejection membrane, max allow out is 3.5 TDS.

So now you need to find what membrane rejection rate you have.

If its a 96% your still good. If its 98%, then your on the border of needing a new membrane.

 

[reefin101]

filmtech...98%. I know I am borderline. that is why I am trying to figure out at what point to change. As I may have another yr or more at 4-5ppm TDS and will keep my filter as is. It is not going thru DI but one canister every 3 mos maybe......

Plus I am still way better than many of the 90% rejection membranes......

 

[MBG75]

filmtech...98%. I know I am borderline. that is why I am trying to figure out at what point to change. As I may have another yr or more at 4-5ppm TDS and will keep my filter as is. It is not going thru DI but one canister every 3 mos maybe......

Plus I am still way better than many of the 90% rejection membranes......

See how long your DI resin lasts with the current membrane. Price out a new membrane.
Figure out which is more cost effective for you.

 

[reefin101]

already done that.....DI still last about the same length of time....which is long and cheaper than a new membrane.

All i am looking for is a number of increase TDS or % that suggests it's time to change for the avg.

 

[BiG-D]

How do you serialize the system?

 

[MBG75]

already done that.....DI still last about the same length of time....which is long and cheaper than a new membrane.

All i am looking for is a number of increase TDS or % that suggests it's time to change for the avg.

You are looking for when the output goes above 2% of what's going in.

 

[AZDesertRat]

This question has been asked and answered many times on the reef forums.
Dow Filmtec membranes may or may not be 98% rejection rate although this is what they strive for. years of lab testing finds most out of the box, brand new are closer to 96-97%. You need to remember, every 2% you lose, you cut the life of your DI resin in half so a 4-6% decrease can add up quickly f you make much water. My off the shelf 75 GPD Dow Filmtec gave me a RO only TDS between 13 and 15, I switched to a hand tested Spectrapure Select series and that 13-15 TDS is now between 2 and 3 using a calibrated COM-100 handheld TDS meter. I have two dual inlines but rarely even tunr them on as the yare in no way as accurate or reliable as a handheld for the same $25. Don't waste money on inlines.

The time to change a RO membrane is when the cost of DI resin starts going up at which time you would be better off with a new high rejection rate RO membrane which could extend the DI resin life by several times for a cost savings and better water quality. For me personally, I use 96% rejection as my change out point as resin starts costing more tyhan the replacement membrane. My current membrane is 4.5 years old and my rejection rate is around 99.4% still to this day.

 

[reefin101]

How do you serialize the system?

here you go. This is what I follow. Taking from BFS.....ut rather than retype! hahah


We recommend sanitizing your RO/DI system approximately once per year. Schedule
this process at a time when you are planning to replace your cartridges. These
instructions apply to water purification systems without a pressure tank. Before
you begin assure that you have about an hour available, and that your work area
and hands are clean.

Turn off the water supply to the
system.

Remove all housings and remove all pre-filters and post-filters
from the system including sediment filters, carbon filters, in-line filters, and
deionization cartridges. Remove the reverse osmosis membrane(s).

Wash
housings with a soft brush or cloth in warm soapy water. Rinse thoroughly to
remove all soap. Don̢۪t forget to carefully remove and wash all o-rings.
Lubricate the o-rings with a small amount of silicone grease and reinstall
them.

Fill each vertical housing with one cup of potable water and three
to four tablespoons of household bleach, and with this sanitizing liquid still
in the housings, screw them back on to the system.

Turn on the water
supply a bit, allow water to fill the entire system, and assure water is flowing
out of the waste line and the purified water line. Place the outlet of the drain
tube and purified water tube slightly higher than the system to assure these
tubes are full of the sanitizing solution. When the sanitizing solution has
reached the outlet of each tube, and with the outlet of each tube placed above
the rest of the system, shut off the water supply for 30 minutes.

After
30 minutes, turn the water supply on and assure that water exits the system from
both the drain tube and the purified water port. Flush the sanitizing solution
from the system for 5 to 10 minutes.

Turn off the water supply and
install new filters, taking care to flush the filters as appropriate.