RODI replacement filters

[6Speed]

I was in one of the old abandon chemistry labs a few weeks ago taking pictures, and noticed they had an RODI unit hanging above the sink. It had really long canisters...like probably 2.5ft long. The DI housing was clear, and the DI looked like it was good. I wonder if it is...? I can't remember if the AC was working in that room or not, though...does it even matter?

I'm sure they're just going to chunk all that stuff when they remodel the building.

 

[twkenny]

I know this thread has kinda run it's course already...but, FWIW...

FilterDirect RODI units are a poor investment. The GE Desal membrane supplied with the FD units is not the best choice for our needs. The horizontal DI chambers are very poorly designed and are quite inefficient.

I made the mistake of purchasing a FD unit and argued that it was the best purchase I ever made. A few years later, I have found that to be far from accurate.
The GE membrane failed early..and the DI chabbers were a pain to refill so often.
I have since (with advice from RC and Bryan at www.purelyh2o.com) replaced my membrane and flow restrictor with a DOW Filmtec 75 GPD and trashed my DI chambers and added a standard, vertical chamber from H2O. I have also had to purchase a TDS meter and pressure guage. All of that would have come with a quality unit. A lot of wasted time and money.

As far as filters, I get mine from PurelyH2o now as well.

 

[Tomoko Schum]

Thanks, twkenny.

My membrane lasted only 11 months which is the original reason that I started this thread.

I have a TDS meter and the water tested fine until just recently. The quality of the water out of my 6 stage Filter Direct unit was fine for 11 months. The only complaint that I have is the length of time the membrane lasted, but it's partly my fault since I didn't change out the other filters at recommended 6 month interval. If I replaced my filters sooner, the membrane would have lasted longer most probably.

I will avoid the inexpensive GE membrane in the future and use better carbon block filters, though.

Is 75GPD membrane the reason for using a different flow restrictor? I noticed that Filmtek has a 100GPD membrane for only $5 more.

Tomoko

 

[AZDesertRat]

Stick with the 75 GPD Filmtec RO membrane. The 100 is only a nanofilter rated at 90% rejection versus the 75 at 98% rejection.

 

[twkenny]

What AZ said.
Your DI resin will last longer with the 75.

 

[Tomoko Schum]

Is upgrading to 75GPD membrane really justified if a 100 GPD membrane produces water with "0" TDS reading?

Tomoko

 

[Tomoko Schum]

How long is your resin lasting? My resin lasted just as long as my membrane.

Tomoko

 

[twkenny]

It's all about input vs. output.
If your incoming water had a very low TDS reading, the 100 GPD would probably be okay.

If your water is 150 coming in, the GE 100 GPD membrane will lower it to around 15. The Dow will lower it to around 3. Water with a TDS of 3 will allow your resin to last a lot longer.
The fact your DI resin lasted that long is a bit odd.

 

[twkenny]

<a href=showthread.php?s=&postid=7826130#post7826130 target=_blank>Originally posted</a> by Tomoko Schum
Is upgrading to 75GPD membrane really justified if a 100 GPD membrane produces water with "0" TDS reading?

Tomoko

The DI resin is what gets it to 0, not the RO membrane.

 

[AZDesertRat]

In Phoenix a 2% increase in membrane efficiency doubles the resin life. That may not be the case everywhere but an 8% increase is significant.
You really need to provide your tap water, RO only and RO/DI TDS readings to know if you would benefit or not. If you are getting close to the 98% rejection level probably not but if you are down in the 90 to maybe 94% range it might be worthwhile.
If your earlier number of 140 ppm TDS tap water is current at 90% rejection you would be sending a TDS of 14 to the DI. If you have 98% rejection it would be less than 3 TDS. If you use the rule of thumb that q standard sized vertical DI filter holds 24 oz of resin and 24 oz of resin will filter 3000 total ppm TDS at 90% your resin will last about 214 gallons and at 98% rejection it will last 1000 gallons. Thats a dramatic difference.
If you are still using the 2x6 oz DI filters the FD units cme with cut those numbers in half, so its 112 and 500 gallons but that is still quite a difference.
Other things you must remember are it all depends on your individual water quality and what the makeup of the TDS is. The most critical thing to remember though is two of the most weakly charged ions and some of the first ones to be released by a spent DI cartridge are phosphates and silicate. Those are two of the reef tanks worst enemies. With a normal handheld TDS meter you need to change resin almost as soon as you begin to see a rise. With an inline its probably too late as they are not as accurate. HM Digital has a new handheld TDS meter that can be calibrated in three different modes and can actually measure down to about 10 megaohms resistivity which is way beyond wah taothers do. I think those meters are going for about $50 most places. It all goes back to the 0 TDS is 0 TDS arguement which is not a true statement. 0 TDS is not 0 TDS unless you are actually able to measure it, 0 can actually be 2% of the full scale of the instrument you are measuring it with as that is the error factor.

 

[twkenny]

<a href=showthread.php?s=&postid=7826177#post7826177 target=_blank>Originally posted</a> by Tomoko Schum
How long is your resin lasting? My resin lasted just as long as my membrane.

Tomoko

I would change/add resin to those tubes every few weeks. Rarely was the output at 0 consistently.

 

[Tomoko Schum]

The current TDS reading of my tap water is 112. I was getting 3 ppm off of the RO output previously. DI unit brought it down to 0. The quality of my water changes from season to season depending on when and where the city of Madison is buying water from, according to the water board of Madison. They mix water from different sources. The mix of water people get depends on what part of Madison they live in. Generally speaking the water quality is better during the summer in Madison due to the fact the city buy a large amount of water from the city of Huntsville to keep up with all the watering people do for their lawn. At one time my tap water read 50 ppm, which really surprised me.

Tomoko

 

[AZDesertRat]

Thats pretty good TDS readings. You might get a copy of your utilities "Consumer Confidence" or annual water quality report and see what the constituents actually are. TDS can be low but if its all nitrates, phosphates or other things thats not so good. Chances are you are in great shape but its wise to research and the report is free.

 

[Tomoko Schum]

I get annual drinking water report every year. They mail it to all Madison residents. Nitrate is very low. Phosphate is not reported (not high), but I measure it because I need phosphate for my fresh water planted tank. The water is very clean according to the report. However, the values are average values. They vary from time to time. Of course I test my tank water, too, and phophate and nitrate in my salt water tanks are always undetectable. All my corals and other livestock seem to happy, too.

Tomoko

 

[AZDesertRat]

You pointed out one of the flaws in the EPA required annual water quality reports. They only have to report what was tested for in that calendar year, so some solutes that were not sampled in that testing cycle may go undetected for as long as three years depending on what it is and how often it must be tested for.
As for averages they have to list lowest level and highest levels obtained along with the average so you should at least have a good idea on the things they list anyway. It always helps to have a friend that works for the utility or like me, I used to get calls referred to me all the time from aquarists since everyone in the City knew I kept corals and fish. I even had a 37 G saltwater aquarium in my City office and another on my admin assistants desk. It seemd like every city employee found their way to my office at one time or another to look at my tank!

 

[Tomoko Schum]

Well, actually I befriended a guy who does the testing by telling him what I was wanting to know all the details for. He was quite curious about how we use the report and what we were wanting to know. I gathered a number of information useful for fresh water planted tanks, then. It's been a few years since I talked with him the last time. I should give him a call.

Tomoko