When to change RODI filters

[gmerek2]

My TDS is at 1 now. Time to change out filters or do y'all let it get a little higher? Which filters do I change?

[epleeds]

I change at 4/5. And change all 4 of mine

[GraffitiSpotCorals]

I change the di resin after the tds starts to show past 1, I change the carbon and micron filters when the tds starts to creep past their normal range. Well I try to at least...

[GraffitiSpotCorals]

Or I change the carbon and micron filters when the first filter looks dirty.

[zygote2k]

easy cheap and smart solution:

change prefilter and carbon filter when TDS out is greater than 10% of TDS in.

If TDS is out is still 5% or more than TDS in, then change DI resin.

If TDS is more than 2%, change membrane.

[flooddc]

Naah! 1 is still good. I only change sediment filter and carbon filter when they look dirty and DI resin when tds reads above 5. Membrane needs replace once every 3 years (unless you do ton of water changes).

I recently replaced everything on my RODI. It's was high (30), came down to 7-8 after I ran it for a 10+ hours. Now still remain around 7.

I replaced with the same brand membrane  (filmtec), but for some reason it not as good as the old one. (maybe it need to break in more).

 

IMO, If you are going to replace them...change them in various stages. Don't change all at once, that way you can quickly detect which new part is not making the cut.  

[L8 2 RISE]

I start replacing filters when I see a TDS of 2.  I have an inline TDS meter and I STRONGLY suggest others use one.  Most come with two meters, one "in" and one "out".  Those aren't the best places to put the meters though, the "in" should go between the RO membrane and the DI cartridge.  I'll go into this later.  The "out" should still go in the product, or "out" line.  

 

When you see a TDS of 2 or higher on the "out" meter, check the "in" meter.  If it is reading 2-3 ppm higher than normal ("normal" varies for each household and system, you have to check when all of your filters are newish, it should be no higher than 12,  for me it is only 3 or 4), then you need to replace your prefilters and/or your RO membrane.  If it is still reading the same as normal, then you only need to replace your DI resin.  You can't always rely on the color changing resin.  This is important and will save you money because, in my experience, I have to change my DI resin 2-3 times per pre-filter change when others would needlessly just replace all the filters.

 

You can often decide whether it is the prefilters or RO membrane that needs replacing based on time (I sharpie the date changed on all of my filter cartridges), as someone else said, if it has been about 3 years, it's probably time to replace the RO membrane, otherwise it should just be the prefilters.  If the "in" TDS remains high after this change, then also replace your RO membrane.  It is important to replace your pre-filters on time because if they aren't working effectively, it will decrease the life of the RO membrane.  

 

Something Tom or someone smarter than me can probably chime in on is if your DI resin has all been used up, continuing to run water through it can cause even more problems because it will allow, or push larger ions through and these can do more harm than normal while not bumping up the TDS more than normal.  Like I said, this is only a topic I've read about, but don't know what truth there is to it and I'm clearly not very good at describing it.  Would like to hear about it though.

 

easy cheap and smart solution:

change prefilter and carbon filter when TDS out is greater than 10% of TDS in.

If TDS is out is still 5% or more than TDS in, then change DI resin.

If TDS is more than 2%, change membrane.

 

Not sure I understand this, TDS will get bad slowly, not an immediate change, also a % of the original TDS isn't a good measure because you don't want a TDS that high to begin with.  My original TDS is over 300, I never let my TDS get higher than 1-2% of that.

 

Naah! 1 is still good. I only change sediment filter and carbon filter when they look dirty and DI resin when tds reads above 5. Membrane needs replace once every 3 years (unless you do ton of water changes).

I recently replaced everything on my RODI. It's was high (30), came down to 7-8 after I ran it for a 10+ hours. Now still remain around 7.

I replaced with the same brand membrane  (filmtec), but for some reason it not as good as the old one. (maybe it need to break in more).

 

IMO, If you are going to replace them...change them in various stages. Don't change all at once, that way you can quickly detect which new part is not making the cut.  

 

There is a problem with your RO/DI units.  If everything is new, TDS should be 0.  Not all membranes perform the same, even from the same manufacturer and there are discrepancies.  I know that Spectrapure tests all of theirs first for this reason, not sure about others.  I suggest replacing your RO membrane.  

[Buckeye Field Supply]

A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the usable life of these two (or more) 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 9much of the 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. Remember that all the water you process, both waste water and purified water, go through the carbon block.

 

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

 

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 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 (collectively called “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 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 the 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 purified water (a.k.a. “permeate”) 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 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 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 purified water more slowly as their function declines.

 

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the TDS in the RO 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.

 

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

 

Russ

[zygote2k]

Sams way and the above way are the ways most likely to generate replacing the cartridges whenever the TDS reads above 1 or 2.

I think this is marketing at best, and in reality a few ppm's of solids certainly aren't going to harm your fish tank or corals. How about all those reef tanks that run on de-chlorinated tap water? They have high TDS and the coral still grows.....

[gmerek2]

LMBO. Well I grew up drinking a lot of unfiltered TDS maybe that's why I'm so crazy and waste big dollars on the tank like a dummy. I heard the RO water will test with a higher TDS after sitting a bit but we all let it sit anyhow. Reef crystals instant ocean salt water says it neutralizes metals since everyone freaks out about them. That always gives me a warm comforting feeling in my belly especially if I decide to run up the TDS

[Origami]

If I'm going to make RO/DI water, I replace (or recharge) my resin with the TDS hits 1 or 2. That's because it's no longer just passing stuff through, it's re-releasing ions that are less tightly bound and replacing them with ions that have greater affinity for the resin.

 

With respect to the other blocks - sediment and carbon - I tend to replace them between 6 months and a year. However, I go through about 2500-3000 gallons of RO/DI per year, so maybe that's not unreasonable.

 

To tack onto Russ' post, it's not always a poorly functioning RO membrane that exhausts DI resin quickly. It also happens with acidic well water with high CO2. The CO2 is too small to be efficiently filtered by the RO membrane and gets picked up by the DI resin causing it to exhaust quickly. DaveS has seen this and, since getting on a well a little more than 2 years ago, I'm seeing it too. It's become really apparent since I've split my mixed bed resin into anion and cation resins. The cation resin that has an affinity for aqueous CO2 (actually CO3-- or HCO3-) exhausts very quickly while the anion resin is slow to exhaust.

[AlanM]

After reading this post I decided to watch my TDS going into the resin when I first turned on the RO/DI today after a week of vacation.  It hovered around 70-80 going into the resin for a while and then settled down to about 3-4.  Still 0 out of the resin.  I wonder if it would help the resin last a little longer if I could put in a little Tee with a valve to drain off that first minute or two of stuff that has been sitting in the filter.  Or maybe the volume is enough that it just doesn't matter.

[Origami]

After reading this post I decided to watch my TDS going into the resin when I first turned on the RO/DI today after a week of vacation.  It hovered around 70-80 going into the resin for a while and then settled down to about 3-4.  Still 0 out of the resin.  I wonder if it would help the resin last a little longer if I could put in a little Tee with a valve to drain off that first minute or two of stuff that has been sitting in the filter.  Or maybe the volume is enough that it just doesn't matter.

 

 Yes, it will last longer. You can also flush the membrane for a couple of minutes before production. That helps to reduce the initial TDS burst. Another way to blunt the effect is to produce larger amounts of RO/DI at one time. This often means waiting until your reservoir is low before starting production.

[Buckeye Field Supply]

After reading this post I decided to watch my TDS going into the resin when I first turned on the RO/DI today after a week of vacation.  It hovered around 70-80 going into the resin for a while and then settled down to about 3-4.  Still 0 out of the resin.  I wonder if it would help the resin last a little longer if I could put in a little Tee with a valve to drain off that first minute or two of stuff that has been sitting in the filter.  Or maybe the volume is enough that it just doesn't matter.

Here's some data from two bench tests with a 75 gpd Filmtec membrane.  That initial burst of high TDS water is common to all RO membranes - caused by a process called "TDS Creep."

 

[matt]

Yeah, I bypass my di and push everything to waste for 2-5m before I start running through my di to the freshwater reservoir.

[gmerek2]

My PPM lasts longer than what your chart says so I flush about 4-5 min to make DI resin last longer. Must be them high quality buckeye field supply RO filters.