artful-dodger
New member
Michael (PotHuntR) asked me in a PM about when and what to change in his RO/DI filter system. Since his PM box is full and this may be of interest to others, I'll just post a general response here:
For starters, here's a link to the Presentation from last fall. (I have made a few enhancements to my system that I'll eventually get noted in the presentation, but the link will remain the same.)
Next, you will need to identify what filter elements you have (or need to have) and the order that water flows through them.
The Filter Guys and other RC sponsor sites offer several variations--you can purchase a pre-designed 3, 4 or 5 stage system or you may, instead, choose to save a bit of money or to customize your setup by buying the components separately. (On a 1 to 5 DIY scale, this is definitely a 1--strictly connect the components with nothing to modify other than cutting tubing to length!)
A generic 5-stage configuration might be:
For starters, here's a link to the Presentation from last fall. (I have made a few enhancements to my system that I'll eventually get noted in the presentation, but the link will remain the same.)
Next, you will need to identify what filter elements you have (or need to have) and the order that water flows through them.
The Filter Guys and other RC sponsor sites offer several variations--you can purchase a pre-designed 3, 4 or 5 stage system or you may, instead, choose to save a bit of money or to customize your setup by buying the components separately. (On a 1 to 5 DIY scale, this is definitely a 1--strictly connect the components with nothing to modify other than cutting tubing to length!)
A generic 5-stage configuration might be:
- Granular Activated Carbon (GAC)
- Sediment (1, 5 or even 10 micron)
- Carbon block cartridge
- Reverse osmosis
- Mixed bed deionization resin (color indicating)
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(The convertible 7/8 stage system outlined in the presentation is nothing more than a variation on this generic design...I run 4 DI stages at the end and use valves to bypass the RO stage during the winter when I can't readily divert the waste water to outside shrub watering.)
Anyone using well water or other water source besides a good municipal water system will probably benefit from running an additional sediment filter as a first stage (before or instead of the GAC).
One point of occasional confusion (especially when buying a used RO/DI system without directions) is the placement of the RO stage. Unless yours is a complete DIY installation, the kit probably has the RO unit positioned horizontally on top of the bracket for the other stages. It needs to be connected, though, in between cannister stages (typically next to last) in the order shown above.
Your system may well be skipping one or more of those--the only one that should visibly appear dirty is the simple sediment element, if that helps identify them.
GAC, if you use it, is loose media like the activated carbon that you might use in a cannister or media bag, but more finely ground and (it is claimed) more refined medical grade. You can either buy replacement cartridges or bulk carbon and load your own. The former is less messy but more expensive, as you'd expect.
According to the Filter Guys' website, activated carbon (whether in a GAC cartridge or carbon matrix) is the primary/best means of removing chloramines that the water systems use nowadays instead of chlorine. There's no way that I know of to tell when the GAC is exhausted and ready to be changed. (If you're running GAC, it should be followed by a sediment filter because it will release a fair amount of black dust.)
The sediment filters are really cheap and I would recommend changing it out every time you do a DI media change. I also see no reason to use anything but a 1 micron cartridge...a larger pore will clog less frequently, but only to the detriment of your much more expensive RO membrane or DI media.
Another useful tip that I picked up during my research is to avoid changing your sediment filter at the same time as your GAC. Since the fresh GAC is guaranteed to release dust, no matter how well you rinse it, wait a couple of days for the old sediment filter to capture that stuff and then swap it out. You'll have a much cleaner looking sediment filter to monitor.
The carbon matrix element is relatively expensive. I've read that they should last up to a year, but that isn't very helpful since one person might make 100 gallons a year and another may make that much a month. Running the extra GAC stage in front should make the more expensive matrix cartridge last longer than if it is the only carbon stage. Again, I don't know of any way to specifically know when it is exhausted. I've (arbitrarily) gone to changing every six months.
The RO element is very expensive but, with proper maintenance and the prefilters, should never need to be replaced. The maintenance requires a bypass valve (cheap...you don't have to buy their kit--the necessary valve and tee fitting are available at HD or Lowes). Once a week (or so), turn the valve for a couple of minutes to bypass the flow restrictor (35 gpd, 75 gpd, etc.) on the output of the RO unit. Bypassing just allows the extra flow of water to flush the membrane of whatever has accumulated, blocking the RO passage of water through the membrane.
The final stage (should always be after the RO has scrubbed the water pretty darn well) is the DI stage. (If you run DI without RO (as I do in the winter) the DI media will need to be changed much more frequently.) The mixed-bed resin that is sold for the hobby is color indicating...that is, it starts out with a mix of blue and gold media, one to capture cations and one to capture anions. As the resin is saturated, the blue crystals will turn brown. The only problem is, that TDS numbers will actually start to rise before it is all brown. If the media isn't swapped TDS will actually rise higher than the tap water you start with as the saturated media releases its load.
As far as accessories, I strongly recommend using one of the inline TDS meters that can, with a push of a button, immediately give you a reading of your incoming and outgoing water. As soon as I see output start to climb above 0 ppm I swap DI. Using a handheld TDS meter works as well, but I know that I used it far less frequently because of the hassles.
That's the all of the important stuff of the presentation in a nutshell!
Gary
