RO membrane

[odin5738]

I'm questioning the quality of my city water. Calcium, Alk, Mg, Nitrate, Nitrtite, Amonia are all fine but my water quality still dosen't seem to be up to par. I think it may have to do with poor water quality from my city water. I moved to a new house about a year ago and I've changed my RO membrane twice and I think it might be going bad again. This will be the third time in a year. The micron filter turns brown sooner than it did at my old house. I've changed it and the carbon block 3 mo. ago along with the membrane. Is there an easy way to check the quality of water from my RO to identfy the problem or rule it out? (RO monitor that's reliable?)

[reef_doug]

I like the hand held TDS meters, I use the Hanna TDS1 and cost around $25. I would post again with your source, post RO and post DI numbers and which filters and membrane you are using.

RO memebranes should last about 2-3 yrs if the prefilters are maintained. Are you using 1 micron sediment and .5 micron carbon block? You might benefit by adding a 5 micron prefilter before a 1 micron or look at the Spectrapure ZetaZorb one.

[odin5738]

I'm using a Maxima Hi-S RO with a 5 micron prefilter and carbon block. The source of my water is Westminster, CO. I'll purchase a TDS tester. What is an acceptable TDS range and do you use it to determine when to change micron filter, carbon block and membrane? The membrane should be changed every 2 to 3 years how about the carbon and micron filters?
Thanks for your input.

[reef_doug]

Prefilter prelacement is really based on usage but every 3-6 months for a 90 gal maintenance would be about right. The purpose of these filters are to protect the membrane from sediment and chlorine/chloramines. A membrane with 96-98% rejection is in good working order. Basically the TDS of post membrane RO product water is usually 6-12 TDS.

Do you have DI after the RO? DI will bring it down to zero. Zero is the goal, I change the DI resin when it creeps up past zero.

Here is Randy's article:
Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm

[odin5738]

I don't have a DI but I'm always looking for advice on the perfect reef system. I've read a lot of Randy's articals on his two part and I'm stating that in a couple of days. As far as my tank set up I have a 90 gal. with a 30 gal. refugium (lights on 24hrs in another room) sump with protien skimmer. No bio-balls. I'm slowly having more success with my reef keeping. If you have any other suggestions please give them to me or questions that may be helpful.
Thanks again

[tmz]

As noted above adding another canister to your ro system with a 5 icron filter will help if your source water is dirty. Adding another canister for dionizqation resin after the ro membrane will reduce the tds (total dissoved solids to near zero) while your ro might be in the neighborhood 8 to 10 ppm.

[odin5738]

I read Randy's artical and everything makes since.
Thanks for your help and thanks again Randy.

[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. 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