Help Please With RO/DI - Filter Replacement Time

I don't know David. It looks like the 3rd cartridge (going left to right) is a filter to me? I have a 2 stage DI on mine and the DI resin in the 2nd cartridge starts changing colors when the first resin is exhausted.

 

That is a 5 stage system, with the following 5 filters (in order of water flow).

1. On the right, is a very filthy sediment filter (this is white when new)

2. One filter to the left, with the white end caps, is a carbon block.

3. The horizontal filter above the bracket is your RO membrane

4. The two filters on the left below the bracket are poorly packed DI cartridges (you can see gaps in the resin bed in each).





Your system takes what are considered "standard-sized" filters measuring 10" x 2.5" (nominal), and your RO membrane is also a standard size (called an "1812" membrane - 1.8" in diameter and 12" long - again, nominal). You can get membranes of the same physical size that will fit into that housing from less than 10 gpd to 150 gpd.


Russ

 

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 filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. The system pictured above doesn't have a pressure gauge - this is an easy low-cost add on. When the pressure drops 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 much 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 cartridge(s), use your total dissolved solids (TDS) meter to measure, record, and track the TDS (expressed in parts per million [ppm&#93 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 1,000 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(s). 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

 

I see that the position of the "in" probe on that TDS meter is in a less-than-ideal location. Remember that you want to know TDS in 3 locations (tap, RO, DI). Because that meter has only two probes, you have to pick two of the three locations to monitor. Of the three posible positions, I'd pick RO and DI. You currently have the "in" probe on the tap water. I'd move it to the line feeding the right hand DI housing. This way you'll have an indication when your RO membrane needs to be replaced.


As an option, realize that there is now a THREE-probe inline TDS meter. In interests of avoiding a commercial post I'll not put a link to it here, but it is called the TRM-1 and looks like this:





Russ

 

Given that you're on well water, I wouldn't invest in a carbon block any higher grade than a 5 micron.

If a 1 micron sediment filter clogs too fast, swap it for a 5 micron, or use a 5 mic followed by a 1 micron.

That black sediment filter makes me wonder if you have issues with manganese. Do you have black or blown staining in your tubs/sinks/toilets?

Russ

 

Not to thread jack but with the info he got and how easy it was to understand and helpful I am now on buying my filters from them!

 

Hope they come on board!!!

 

Sounds like a win-win all around! Blackx-runner - we emailed you earlier this morning re the sponsorship.

Russ

 

Just sent a link to several people in our area (Des Moines) that are struggling with replacing membranes. This was said very very well!

I am all about changing my filters source water is a huge part to getting the tank thing right!