Do I need to replace my RO/DI filters if TDS is still 0?

[todd141]

As the title says.....My ro/di unit is more than a year old, but I still get 0 readings from my TDS meter.

I've always read you should change out the filters at least once a year. So, my question is...If I still am getting a 0 reading on my TDS meter, do I need to replace the filters?

I have a 75G tank and a 15G refugium, and change about 10 gallons of water a week.

Thanks in advance for any input.

Todd.

[todd141]

I forgot to add - if it makes any difference - but my unit is an Air, Water, Ice Typhoon 5 Stage RO/Di unit.

thanks again...

[BuckeyeTodd]

if it ain't broke don't fix it

[Soymilk]

Check your water pressure at your membrane and try getting a tds reading before your di unit. This will let you know if you have to change your filters.

Its up to you though. Cuz right now it's still working, worst case scenerio right now is you could be depeleting di faster than normal.

[solitude127]

Originally Posted by BuckeyeTodd

if it ain't broke don't fix it

I totally disagree. The prefilters play an important role in ensuring that the membrane lasts as long as possible. Prefilters are inexpensive compared to the membrane.
Here's a good thread from a while ago about RO/Di filters
http://www.reefcentral.com/forums/sh....php?t=1415770

[oscar.millan]

Sediment and carbon should be changed regardless of TDS = 0.

That's the RO part. DI doesn't need to be changed until it's exhausted.

I don't blame you for not knowing, I don't always read the owners manual either, but it's an important note when you own a RO/DI unit.

+1 on the previous post.

[oscar.millan]

Sediment and Carbon every six months or so.

[oscar.millan]

I couldn't disagree more, but we are all entitled to our own opinion. Although I try to only chime in when I'm certain about something. If I'm guessing I will defer to an expert.

Originally Posted by BuckeyeTodd

if it ain't broke don't fix it

[oscar.millan]

I agree with the first part, once the sediment filter gets clogged water pressure will go down.

But that doesn't account for the Carbon block, which removes chlorine. Chlorine is what eats away at your membrane.

Worse case scenario, you're prematurely eating away your expensive membrane.

Hope that helps!

0scar M.

Originally Posted by Soymilk

Check your water pressure at your membrane and try getting a tds reading before your di unit. This will let you know if you have to change your filters.

Its up to you though. Cuz right now it's still working, worst case scenerio right now is you could be depeleting di faster than normal.

[chadfarmer]

depends on the water going into the unit

[oscar.millan]

This is true, although most of us don't have access to natural mountain springs.

Most water reports will show TDS, chlorine, etc. This will help narrow down the "depends" part of the question.

Originally Posted by chadfarmer

depends on the water going into the unit

[Drez]

Originally Posted by Soymilk

Check your water pressure at your membrane and try getting a tds reading before your di unit. This will let you know if you have to change your filters.

Its up to you though. Cuz right now it's still working, worst case scenerio right now is you could be depeleting di faster than normal.

This is true and should be taken into account, I would take off the DI unit and test the TDS, if your getting down to ~5-6 then your fine, if its much higher your making the DI resin do too much of the work and resin is more $$ than prefilters.

Prefilters can be rinsed too btw

Keep in mind most RO/DI units are made for higher usage than most of us use them for. Unless your using for drinking etc. also. So we can usually take the user manual as a fairly conservative est.

[todd141]

I didn't even think about depleting the membrane faster...I will check TDS before the membrane.

thanks everyone for your posts.

[The Grim Reefer]

I just read the TDS on fresh filters before the membrane and when they start increasing change the filters. My last filters were still doing good past a year and the dual DI cartridges hadn't been exhausted yet either. Of course I didn't do many water changes so your system size and number of water changes you do will make a big difference.

[Buckeye Hydro]

A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the useable life of these two filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. This is your indication one or both of the filters is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. A good 0.5 micron carbon block for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. Some original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons.

Regarding your RO membrane and DI resin, use your TDS meter to measure, record, and track the TDS (expressed in parts per million) in three places:
1. Tap water
2. After the RO but before the DI
3. After the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 parts per million (ppm). Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block filter (collectively called “prefilters”) 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 it is still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce less purified water (aka “permeate”), but have a higher rejection rate (96 to 98%). The life span of a RO membrane is dependent upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the total dissolved solids (TDS) in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce less water as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the 40 ppm water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm, you know that your resin needs to be replaced. Sometimes people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty” water. This will exhaust the resin quicker than would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!
Russ

[oscar.millan]

I'm having trouble understanding what advice if any is given. Particularly in the first paragraph, as I read it you're asking to test the TDS after the RO membrane.

If your starting TDS is 1000 and you have a 98% rejection rate, you will never get down to ~5,6 TDS. ( 1000 TDS 98% rejection = 20 TDS)

If your start at 500 (500 TDS @ 98% rejection = 10 TDS)

By that example the input TDS would have to be around 250 to achieve the ~5,6 you are suggestion.

(250 TDS @ 98% rejection = 5 TDS)

My comment is basically to understand what, if anything you are suggesting can be done if you're TDS is above said mark (5-6 TDS). For those of us with hard water, there isn't much that we can do, and resins will likely be used up more quickly. By your measure, I haven't been "fine" for years as my TDS constantly reads at 10 TDS after the RO membrane. Any thoughts?

Originally Posted by Drez

This is true and should be taken into account, I would take off the DI unit and test the TDS, if your getting down to ~5-6 then your fine, if its much higher your making the DI resin do too much of the work and resin is more $$ than prefilters.

Prefilters can be rinsed too btw

Keep in mind most RO/DI units are made for higher usage than most of us use them for. Unless your using for drinking etc. also. So we can usually take the user manual as a fairly conservative est.

[oscar.millan]

TDS before your DI will only tell you how well your RO member is performing, it will not tell you the state of your sediment filter or carbon filter.

+1 on the water pressure as it is affected by the clogging of the pre-filter.

One point that is often overlooked is the carbon filter which removes chlorine. Again, this will eat away at your RO membrane. I replace every 6 months to be safe, only way to know exactly when to change it is to test for the chlorine after the carbon block.

Originally Posted by Soymilk

Check your water pressure at your membrane and try getting a tds reading before your di unit. This will let you know if you have to change your filters.

Its up to you though. Cuz right now it's still working, worst case scenerio right now is you could be depeleting di faster than normal.

[oscar.millan]

Thank you, well said.

+1 This should answer many of your questions, and it's right on the mark.

Originally Posted by BuckeyeFS

A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the useable life of these two filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. This is your indication one or both of the filters is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. A good 0.5 micron carbon block for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. Some original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons.

Regarding your RO membrane and DI resin, use your TDS meter to measure, record, and track the TDS (expressed in parts per million) in three places:
1. Tap water
2. After the RO but before the DI
3. After the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 parts per million (ppm). Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block filter (collectively called “prefilters”) 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 it is still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce less purified water (aka “permeate”), but have a higher rejection rate (96 to 98%). The life span of a RO membrane is dependent upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the total dissolved solids (TDS) in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce less water as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the 40 ppm water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm, you know that your resin needs to be replaced. Sometimes people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty” water. This will exhaust the resin quicker than would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!
Russ

[pattim]

The actual fact is that the RO membrane *only* specializes in removing ionic species, like iron, calcium, etc. (i.e., *dissolved solids* - hence "TDS"). The purpose of the charcoal filter is to remove organics, benzene, toluene, etc.; any other organic product of life (or death/rotting or manmade pollution - of which there is *much* these days). So it's important to change those on schedule, and your TDS meter does NOT measure those chemicals. This is ESPECIALLY important if you live in or near a city (or, for instance, a frakking site, where they put anything toxic they want into their fracking fluid), where lots of organic toxic materials are in the water sources.

Do NOT neglect the carbon filters!!!!!!!!!!!!!!

The only way to detect these organic poisons/contaimnants is complex analytical techniques, either specific to a particular organic contaminant, or else FTIR or ICP. Most of us have no access to these. Change your carbon filters independent of TDS.