RO no DI = TDS?

[NaCl_H2O]

Ok, I'm gonna need to eat my words from prior posts, but my DI cartridge seems to have gone south fairly soon.

With the DI removed, what TDS should I expect?

#1: 1 Micron sediment filter
#2: .5 Micron Carbon Block filter
#3: RO membrane
#4: Empty

TDS = ???

Is it helpful to put maybe a .5 Carbon filter in the #4 slot?

Thx - Steve

[JimD]

15/20 tds... In that area, the lower the better. A DI cart will give you a TDS of zero by itself, not for long though... The RO membrane and pre-filters help extend the life of the DI.

[captexas]

I would try to replumb it from what you have listed. Having a filter other than the DI after the RO membrane is not very affective. You should filter out as much as you can then go to the RO and then to the DI. My filter has a 10 micron sediment filter, then 5 micron cabon filter, then 1 (or 0.5?) micron carbon filter, then the RO membrane, and then the DI filter. From what I have read, having too small of a micron filter at the begining chokes down the pressure that your other filters need to work properly.

[Instar]

I use a 0.5 to 1.0 micron sediment prefilter, 1 micron carbon block, then the RO without a DI. I get less than 14 TDS. Had the same system for years, gets plenty of water out. A prefilter that is changed, not plugged up, should not act as a pressure block to water flow/cut pressure once its wet. Pressure in the lines may vary due to more than normal use such as laundry, neighbors watering, etc. Time of day and day of week can make a difference on pressure in the lines but once the pressure is in the RO unit and filter cartridges, its there. I even have my incoming line valve cut half way back to reduce flow some and still get a little more than what the output of my RO is rated for. The point of the prefilter is to keep the carbon block from getting any sediment particulate that would restrict its function. My water changes the color of the prefilter and thas how I gauge when to replace it. If you are blowing your DI rather quickly, perhaps you are dealing with chloramines and not chlorine. If thats the case and the RO membrane is compromised, theres not much you can do except replace it with a twin tower chloramine, 5 stage RO/DI unit. Well this ought to open up a can of worms.

[alexwolf]

I have a DI cart here Steve if you need one, theyre the cool refiullable kind.

[JimD]

If my post RO was 30, Id trash it! 20's pushing it... Mines right at 10-12 with a 98.5% rejecion rate.

[captexas]

Depending on the RO membrane, the rejection rate can vary, usually maxing out at about 99%. So . . .the TDS you have remaining after the RO is dependent on your total TDS levels, quality of the RO membrane, and the the life left in that membrane. RO membranes don't last forever and should be replaced every 2 to 4 years depending on usage.

[JimD]

Input source TDS = (X)
Post RO TDS = (Y)

[(X-Y)divided by X] x 100 = Rejecton rate.

Josh, a 97% rejection rate for a 100gpd membrane would most likely be an exception, normaly theyre in like the 90% range. I just installed a Spectrapure Select membrane rated for 60gpd and its giving me zero tds post DI. I noticed that you got a refillable DI cart from Buckeye,,, Make sure you install it with the arrow pointing UP! lol, I had it pointing down and couldnt fugure ut why my post DI tds was the same as my post RO tds... lol, can you say DUHH!!!

[Instar]

This is exactly how they're supposed to be setup

Thats not how the ones come for reefs from Kent. Also, if that was true then it would be difficult to get a good 1 micron prefilter from the reefs stores but the more elaborate reef stores carry the better grade 1 micron prefilters. The cheaper RO units that HD carries have larger micron prefilters like 10 to 20 or more. The more expensive units come with the 1 micron prefilter. Why would you allow sand and crystalline sediment to get through anyway? Both the units I bought came with 1 micron prefilters installed first in the line. They are however more expensive so maybe that is at least part of the theory that contributes to the larger micron size being the "right" one. I've already had my main unit longer than the "expcected" life span so I am not changing to a larger than 1 micron prefilter until there is some real proof of the "correct" way being a 20 micron prefilter (which is a lot cheaper). Why would there even be a more expensive prefilter if it was not the way to use them? Do you have references regarding using the cheaper prefilters over the more expensive 1 micron ones? That would be interesting to me as the cheaper 20 micron prefilters are available at HD too.

[captexas]

I don't see anyone mentioning using a 20 micron filter. The "cheaper" ones at HD are for drinking water, not what you put in your reef tank. And as you know, everything associated with this hobby automatically gets a price increase. As far as the wide range of filters available, it's all in how you set it up and what you want to get out of it. I have a catalog from Farriswater.com and the section on filters cartridges alone is 15 pages long! The differences in price are also related to the materials used, not just the micron rating. Certain materials work better and last longer. The Spectrapure filters cost a lot more than any others for some reason. Do they work any better? That would have to be determined by a long-term test.

As for the filter setup goes, say your tap water has contaminants with the largest being 15microns in size. If you have a 1 micron filter at the first stage, it is having to filter out everything from 1 to 15 microns, which is a lot of junk. Then in the second stage you have a 0.5 filter so it is taking out very little. Your first cartridge is going to get used up quickly and eventually leach junk through into the second filter and so on.

Now, with the same tap water, you have a 5 or 10 micron filter first, it is taking out a lot, but not everything. Then the second filter of 1 micron takes out more without being overwhelmed. Then a 0.5 micron filter after that is able to get out all the really small stuff without being clogged up by the junk that should have been removed in earlier stages. Basically, you want to place the workload evenly on the filters instead of wearing ne out so quickly.

[Instar]

Manufacturers Product Recommendations:
Kent RO: Incoming water TDS, chemisty, pressure and temperature affect the effluent output quality and quantity. Since we are only talking about the prefilter micron size and carbon block micron size, that is what I will address from the product literature. 10 and 20 micron prefilters will allow diatoms, bacteria (coliforms), micro organizms and sediment through into the other filters for colonization and degrading performance of those other filters. Iron, calcium, mg (fowling chemicals) will reduce the life of the membrane exponentially*.

Units performing to 98%-99% purification, full size units: The manufacturer calls for part number CF1M - 1 Micron Prefilter. For the carbon block; Manufactuerer calls for part CFCE solid block carbon (0.5-1 micron)*.

In the small 2 stage, the "bare bones" units (just one filter and simple membrane) the manufacterer calls for IFCE - 5 Micron carbon block before the membrance matrix*.

We test the water effluent in the lab to be sure there is no bacteria that gets through or grows in the water. In regard to the prefilters I am afraid we will have to respectfully agree to disagree. Definitely don't want slime and bacteria growing in the second stage towers if I can help it so I will stick to the product recommendations and the stds we use to make water like this in the commercial labs.

*Copyright Kent Marine, 1999. Rev.2

[NaCl_H2O]

FWIW, I re-plumbed my unit as follows:

#1: 1 Micron sediment filter
#2: 2nd 1 Micron sediment filter (They are cheap :) )
#3: .5 Micron Carbon Block filter
#4: RO membrane
xx: No DI Cartridge

If I can trust my cheap TDS meter, the result is 18ppm - I'm happy :D

[JimD]

There ya go! Post Ro tds between 15 and 20. Youre right where you need to be, now get a DI cart and youll be at zero! Excellent! Whats the membranes rejection rate?

[NaCl_H2O]

If I can trust my cheap TDS meter ...

I have This One (http://www.marinedepot.com/md_viewItem.asp?idproduct=RO1312), and have both probes reading off the output side. One probe reads 18ppm, the other jumps around 25-40?

I honestly don't trust this thing other than for relative numbers. I already tossed one like this that went bonkers.

Anybody know of a good & reliable TDS meter?

No, Larry, I can't spend $250,000 on one :o

[JimD]

www.H2Oinstruments.com
Ive been using Hanna tds meters for years, cheap but reliable.

[Instar]

No, Larry, I can't spend $250,000 on one

If you spend even half that, I'm coming over to help you get your moneys worth out of it. :lol


#1: 1 Micron sediment filter
#2: 2nd 1 Micron sediment filter (They are cheap )

You would be better going with a 2nd carbon block than 2 prefilters. One prefilter is all you need. If you have courser sediment in your water or lots of it a separate unit with a strainer and maybe something like a 10 micron prefilter would be useful. But, where you are thats probably not an issue unless new home starts is causing the water company lots of new pipe work in the mains. If you use a single 1 micron prefilter and 2 carbon blocks at 0.5 microns then you will basically have what we all got in the group buy from AquaFx. (They recommend a 1 micron prefilter and say that using the correct filters will greatly extend the life of your RO unit.)

[Instar]

There is nothing wrong in the logic of all that Joshua except in the prefilter winding itself. It does precisely that, a staging from larger particles to smaller, within the winding the only difference is in the end particulate size coming out into stage 2. At 10 microns, this lets things even as large a blood cells through, bacteria including coliforms (surely everyone is familiar with that in the water source), molds, slime molds, diatoms, pollen, smaller scaling particulates from the pipes re: our hard water. This means stage 2, the first carbon block will be a contaminated filter stage and this is not desirable in ultra purification systems. The one we use in the lab doesn't loose pressure even after the filters are old. If the carbon block gets contaminated with such small organics as diatoms and bacteria, it will become much less effective. If the effect is great enough, chlorine can get through to the membrane and that will destroy it. Then you will not need prefilters, you will need a membrane and have to change your DI material frequently to maintain a 0 TDS. So, either change the prefilters more or risk compromising the membrane and DI? My water has to be the crappiest water around out here and I don't plug my 1 micron prefilters even after what I consider extended use. They are 6 or 8 bucks and that seems like a worthwhile investment to me a couple times a year. What airwaterice says is true however. If you are going to stage filter sizes, getting progressively smaller is the way to do it. Since coliform bacteria do get through a 10 micron though, this is of no or limited benefit for an RO system and it will cause the efficiency of the first carbon block to be decreased after some use. This might be ok in systems that have 2 carbon blocks because there is the safety of the second for contact time. Rest assured if cholrine or chloramines get through to the membrane in high enough concentration, they will cause it to output higher TDS into the DI cartridge and that life expectancy for the DI will be shortened. Such chemicals contacting the membrane of the RO unit will ruin it in a short time. If you never have TDS issues with your current method and your DI lasts a long time producing 0 TDS, then you have it correct for your water source but once you ruin your RO membrane, there is no undoing that. You replace you unit. From what I read on here people are burning up their DI's fast and have high TDS issues all the time. There is no way to keep coliforms and spores and all that other junk out of your RO system except with a 1 micron prefilter. Granted there may not be much of it at some times of the month, but any is too much. If you have a well, use a strainer/prefilter (10 microns) unit before the entire RO/DI unit. I recently tested my water without RO against another very experienced reefers water who had a 4 stage (mine is an old 3 stage) and my water was 12 to 14 TDS without any DI cartridge to his at 49 to 51 TDS with a DI cartridge. Perhaps this is not a fair comparison because the membrane quality can vary a lot in units with different ratings.
Its been fun trading data with you. It seems the self proclaimed water guru is not in agreement with Kent or AquaFx representatives. I wonder what the culligan engineer would say and the contractor we use at the hospital? When I contract for the water for lab, dialysis and pharmacy, its nothing but the best. I think my reef deserves the same, its at least as expensive as all that.
Well, we still disagree. Thats half the fun of this hobby. 8)

[Instar]

Can you briefly explain how coliform and bacteria destroy the carbon block?

Briefly: Very small contaminating bacteria from waste treatment gets through all of our water treatment filters and means and grows in the carbon block, plugging the pores and preventing partially the adsorption of chemicals and disolved organics. Even if its dead, its only a couple microns so it plugs the carbon block a little. If there is a carbon block strainer thing, I don't know at what particulate size that would be? I'd like to know if you know that?

Your new membrane will likely be a higher grade as well as larger surface area. If it is a higher grade. more expensive membrane matrix, then you will get a lower residual TDS. After spending all that money, the only way to keep it there is to make sure you change all the prefilters and prevent contact with water treatment chemicals and all sediment. Thats probably why these companies sell the reverse flush kits to clean out the smaller than 1 micron sediment that gets through to plug the membrane. Rather than risk that I'd use the 1 micron prefilters and get it all trapped up quick. That doesn't affect pressure BTW, it affects flow (another can of worms to open). The membranes will loose performance output if the units go from your 65 PSI (or more) incoming water line to the 35 PSI incoming range. You can see and feel lower than 65 water pressure in the afternoons. When that happens, don't make RO/DI water at that time just to be on the conservative side.

If you don't want those 1 micron prefilters and they are sealed in a wrapper, I'll buy them from you. I've never had one even partially plug up. I change them a couple times a year. I probably should start changing them more often cause the new housing subdivision starts are going on like crazy here.

[Instar]

It will be interesting to find out how much difference your new membrane makes in regard to the life of your DI cartridge.

[NaCl_H2O]

Well, this thread has turned into a debate ... I love this site! MAASTards are so predictable :P

Ok, I am considering adding a fifth stage (DI) canister but using the refillable type cartridge. I see both "Anion" and "Cation" resins available on-line. Which do I use, or a mixture? Is a mixture what Kent sales as their "Color Changing" DI cartridge?

[captexas]

Steve - a "mixed bed" DI resin is a mixture of anion and cation resins. There are also different grades of resin, some listed as medical grade, semiconductor grade, and nuclear grade. I have no idea what the real differences are between them.

[JimD]

Big difference! Nuclear grade is the only way to go. Most lfs's use medical grade resin, Take a tds meter with you next time you go and measure the RO/DI water they sell... lol! You may be suprized...

[NaCl_H2O]

Here is another question for the RO/DI crowd. Can your water pressure be too high? Just noticed on my Kent instructions that 85 psi is "Ideal". I have GREAT water pressure and the guage on my RO/DI unit reads 120+ :o I cut back the valve feeding the unit to drop it to 85 psi, and my output TDS dropped :) Since I have been running with 120+ psi, have I damaged the membrane? It is a 60gpd Kent membrane.

[Instar]

Over 120 is way over. You need a pressure regulator for your entire house if that reading is correct. Your plumbing and sink fawcet valves may fail you at too high a pressure. Good that you cut it back for your RO. The higher pressure, to a point at least, will give you better output but they do have a rating. The manufacturers make pressure pumps to boost pressure to get more production, but, over 120 seems excessive to me. You have to check the rating for your membrane and see what it is. Makes sense the TDS would drop if you lower pressure but a half open valve is not a perfect solution. Get a regulator if you want it right.

Joshua, all membranes are not created equal. Some allow nearly 5% of the solids to pass through, others allow kess than 2% at their specified temperature and pressure. Different companies may use the same brands, but, there are different performance specs for different rated membranes. Thats coming from Kent lit, so if others buy from one source, maybe they all buy only one grade? Theres a lot of sales hype over all this too and that throws off the real facts of the matter.
Since your prefilters don't keep size, thats probably not what I am interested in. Mine stay what they are always, wet or dry.

[NaCl_H2O]

www.H2Oinstruments.com
Ive been using Hanna tds meters for years, cheap but reliable.

Just in case someone is still trying to find that perfect gift for my birthday :D

http://www.h2oinstruments.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=HOS&Product_Cod e=C99

[BuckeyeHydro]

The following may be of some help in this discussion. Although it was prepared to answer the question: "When should I change my filters?" it also covers the issue of pre and post system tds levels as well.

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 filers is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. The Matrikx+1 for example will remove >90% 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 ppm. Common readings are 100 to 400. So for sake of discussion, let's say your tap water reads 400. 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 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 permeate, but have a higher rejection rate (98%).

If you measure the TDS in your system after the RO membrane, and before the DI housing, you'll be able to measure the rejection rate of your membrane. A declining rejection rate is a good way to tell when your membrane needs to be replaced.

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. Usually 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.