r/o system

[jc]

My r/o is reading 71ppm on the tds meter. Do all the filters have to be replaced all at once? I have a 6 stage system and to replace all of the filters would be the same price as buying a new system. Was I supposed to change the pre-filter or carbon blocks sooner to make the r/o membrane last longer?

[hobogato]

check the water coming out of the RO membrane - that will tell you if it is bad. if your DI is used up, it will start to release stuff back into the water and inflate the TDS

[jc]

I'll do that, thanks.

[jc]

I made a mistake the r/o TDS is 27 ppm. The water coming out of the membrane is 24 ppm. Almost all of my DI resin is dark now. If I change it out will it take me down to near 0 ppm?

[hobogato]

it should :)

[JimD]

If the water coming out of the r/o membrane is 24ppm, the membrane is on its way out. Although replacing the di will most likely bring your tds back to zero, it wont last nearly as long as with a membrane tds of say 12 ppm which is approximately where it should be.

[jc]

Is there a way to tell if my carbon filters are still taking out chlorine? If my RO water still has chlorine would it dissipate if most of it goes into the protein skimmer?

[caferacermike]

If my RO water still has chlorine would it dissipate if most of it goes into the protein skimmer?

It would in a few hours however most municipalities now use Chloramine which is stable up to a minimum of 6 months. Doesn't matter if you leave it out, boil it, stir it, whatever, it is still in there. The fact that it is that tough is exactly why our municipalities are switching over to it. Check with your water provider.

[jc]

The SAWS website only list chlorine.

[hobogato]

If the water coming out of the r/o membrane is 24ppm, the membrane is on its way out.

not so here in sa jim. my membrane runs 22 to 25 new. our water is around 300 TDS out of the tap, so that is about right for a membrane that rejects 90% or so

jc, i run two carbon filters - one block and one granulated

[JimD]

A good membrane with a rejection rate of 95% should be much less than 25ppm. My membrane is rated at 98% and the ro output is right at 12ppm. I can see where a lesser rejection rate would give a higher ppm though. Anything above 75gpd will offer a lesser rejection rate usualy in the 90% range. Whats your units output?

[hobogato]

you're right jim, mine's 100 gpd.

[BuckeyeHydro]

This may help:

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. The Matrikx+1 (“Chlorine Guzzler”) for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. 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 its 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 dependant 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 to 3 ppm, 5 ppm, and higher, 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 then would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!

Russ