Im looking into buying an rodi unit. I have a 9g aquamedic anano and a 55g tank, so my water needs are low. I was wondering if you know of any low gpd ro units that I can look at. I have a low budget, and I dont want to spend a ton of mony on a high gpd unit that will never get utilized to its potential.
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RODI advice
- Thread starter ocmsolidsnake
- Start date
An RO/DI unit is one item that can generally be shopped for by price, as long as it meets some minimum requirements.
One thing that you will find is that a small unit, say 25 gpd, costs almost as much as a 100 gpd unit, assuming all the features are the same. So the choice for you becomes one of saving a little money, or getting the larger unit for only a little more.
I would look for a 4 stage unit, consisting of a particulate filter, a carbon filter, the RO filter, and the DI filter. nice options are a TDS meter, and a bypass valve, but you can add these later.
Parts are generally standard, so you usually can use replacement filters from one manufacturer in another manufacturer's unit.
One thing that you will find is that a small unit, say 25 gpd, costs almost as much as a 100 gpd unit, assuming all the features are the same. So the choice for you becomes one of saving a little money, or getting the larger unit for only a little more.
I would look for a 4 stage unit, consisting of a particulate filter, a carbon filter, the RO filter, and the DI filter. nice options are a TDS meter, and a bypass valve, but you can add these later.
Parts are generally standard, so you usually can use replacement filters from one manufacturer in another manufacturer's unit.
This is a tough call in my opinion. With only 9 gallons of total water space not including rock, sand, etc you don't have a very big water demand. You might find it easier to just purchase distilled water from the grocery store in 1/3/5 gallon containers.
The RO/DI unit may not be worth the hassle. You need space to store it, a place to hook it up when you need to use it. Some type of storage container to collect the water in, a TDS meter of some kind to make sure it's working correctly. RO/DI units don't like to be left sitting around not getting used and tend to "gump up". With only a 9 gallon tank you're not going to use the RO/DI very much.
By the time you factor in the cost of the replacement sediment and carbon filters, DI resin and membrane replacement when it's time you'll probably find there isn't going to be a great deal of cost difference per gallon based on what you use. The RO/DI water could end up costing you more then distilled water from the grocery store.
I just wanted to play "devil's advocate" on the purchase to make sure you really want to buy one and not think you "need one". Distilled (not spring or other bottled water) is every bit as good for your current purposes as RO/DI water.
Now with that being said, if you know you are going to be getting another tank or upgrading to something of at least 30 gallons or bigger then the purchase of an RO/DI system makes a lot more sense as it will be cost effective in that situation.
I agree with what DaveK said except I would stay away from 100gpd systems. The typical membrane used in the 100gpd systems is different then the 50,75,150gpd membranes and has a far lower rejection rate which translates to allowing more TDS to pass through the membrane which is what you don't want. This will put a much larger burden on the DI stage which you'll go through about 3 or 4 times faster and this add up quickly in $$$.
Good bang for the buck systems in my opinion are AirWaterIce.com. Spectrapure.com are about the best but very pricey and the hardware itself is no better then AWI models. Spectrapure hand selects membranes for high rejection rate which can save you money in the long run on DI use. Another popular vendor is TheFilterGuys.biz but I'm not a big fan of the hardware itself. Not quite as good in layout as AWI.
With that said the heart and sole of the RO/DI unit isn't the hardware but the filters used in it. I can't make a recommendation as to how many stages you need without knowing what your tap water is like to begin with.
Do you know if you water department uses chlorine or an alternate? This is very important. Obviously if you have a well this doesn't apply. Also important is knowing both the pH and Alk level of your tap water. Knowing the answer to these 3 questions is the key to figuring out the amount of CO2 in the water and what type of filters/membranes to use in the RO/DI water to properly process the water.
Carlo
The RO/DI unit may not be worth the hassle. You need space to store it, a place to hook it up when you need to use it. Some type of storage container to collect the water in, a TDS meter of some kind to make sure it's working correctly. RO/DI units don't like to be left sitting around not getting used and tend to "gump up". With only a 9 gallon tank you're not going to use the RO/DI very much.
By the time you factor in the cost of the replacement sediment and carbon filters, DI resin and membrane replacement when it's time you'll probably find there isn't going to be a great deal of cost difference per gallon based on what you use. The RO/DI water could end up costing you more then distilled water from the grocery store.
I just wanted to play "devil's advocate" on the purchase to make sure you really want to buy one and not think you "need one". Distilled (not spring or other bottled water) is every bit as good for your current purposes as RO/DI water.
Now with that being said, if you know you are going to be getting another tank or upgrading to something of at least 30 gallons or bigger then the purchase of an RO/DI system makes a lot more sense as it will be cost effective in that situation.
I agree with what DaveK said except I would stay away from 100gpd systems. The typical membrane used in the 100gpd systems is different then the 50,75,150gpd membranes and has a far lower rejection rate which translates to allowing more TDS to pass through the membrane which is what you don't want. This will put a much larger burden on the DI stage which you'll go through about 3 or 4 times faster and this add up quickly in $$$.
Good bang for the buck systems in my opinion are AirWaterIce.com. Spectrapure.com are about the best but very pricey and the hardware itself is no better then AWI models. Spectrapure hand selects membranes for high rejection rate which can save you money in the long run on DI use. Another popular vendor is TheFilterGuys.biz but I'm not a big fan of the hardware itself. Not quite as good in layout as AWI.
With that said the heart and sole of the RO/DI unit isn't the hardware but the filters used in it. I can't make a recommendation as to how many stages you need without knowing what your tap water is like to begin with.
Do you know if you water department uses chlorine or an alternate? This is very important. Obviously if you have a well this doesn't apply. Also important is knowing both the pH and Alk level of your tap water. Knowing the answer to these 3 questions is the key to figuring out the amount of CO2 in the water and what type of filters/membranes to use in the RO/DI water to properly process the water.
Carlo
Right now im buying 7 gallons of distilled water a week for water changes. So i think a rodi will pay off. So am i safe if i go for low gpd if it saves on cost?
Personally I would buy a RO/DI unit. I have 3 tanks- a 46g, 16g and 7g. I got lucky (after spending hours scouring the fish classifieds) and was able to get my hands on a Spectrapure 60gpd for a little over $100. I was happy with 60gpd because I read that there is less waste with a unit that produces less gallons per day and it's cheaper even when purchased new.
I was buying my water at Walmart and it quickly became tiresome driving back and forth and I was getting paranoid that I looked like a nutty survivalist waiting for the world to end ;D Then there are the days you can't get to the store to buy water when you are running low. God forbid you had to do an emergency water change. From past experience,just try buying water when the forecast is for 3 inches of snow!! I went to the store to find the shelves bare. I felt like screaming "What's wrong with you people, What about my poor fish. I need water for a water change!!!!" It's not like we are going to be housebound for a week.
Then I had to lug the 16 gallons inside and find a place to store them. I'm sure the guys who collect the recycleables were wondering what heck was going on at my house when they saw all the empty water containers.
Finally having my own RO/DI allowed me to have total control over my water quality. That was a nice feeling.
I was buying my water at Walmart and it quickly became tiresome driving back and forth and I was getting paranoid that I looked like a nutty survivalist waiting for the world to end ;D Then there are the days you can't get to the store to buy water when you are running low. God forbid you had to do an emergency water change. From past experience,just try buying water when the forecast is for 3 inches of snow!! I went to the store to find the shelves bare. I felt like screaming "What's wrong with you people, What about my poor fish. I need water for a water change!!!!" It's not like we are going to be housebound for a week.
Then I had to lug the 16 gallons inside and find a place to store them. I'm sure the guys who collect the recycleables were wondering what heck was going on at my house when they saw all the empty water containers.
Finally having my own RO/DI allowed me to have total control over my water quality. That was a nice feeling.
JohnS_323 said:
Darn eyes playing tricks on me again. Totally missed the 55g tank. Well now it's safe to say a RO/DI unit will pay for itself. Otherwise the post is pretty accurate for the person with only a small nano tank.
A great way to buy is used if you happen to find one available. RC seems to always have them online there for about half a new unit. It's really the filters and membrane that make the system and not the hardware per say. Yes you can get all kinds of "extras" like PSI gauges, TDS meters, DI Bypass for drinking water, etc built in but you can add these to any system.
As a general statement all RO/DI units are built the same. The difference between a 50 and a 150 gallon per day system is the membrane (and flow restrictor) itself. You can change these on any system to increase or decrease the rate. Bigger isn't always better. Ideally you want to "size" the unit so it gets used every 3 days or so and at least once a week. Getting a "big" unit that you only need to run once a month is a very bad idea as the membranes will clog up and foul quite quickly if this pattern of running is used.
The flow restrictor is a couple dollar part. The membrane will cost between $30 & $100 depending on where you purchase it. The restrictor never needs replacing unless you change the flow rate of the membrane. All it does is create back pressure on the membrane. It's this back pressure that keeps the membrane clean. Almost all membranes we purchase for our RO/DI units are designed to optimally run at 4:1 which means you waste 4 gallons to get 1 gallon of pure water. That an efficiency of 20% or 1/5. If you think this is to much waste you can add a second membrane to the system as a piggy back and feed the waste line from the first membrane to the second membrane (sized the same gpd as the first) and basically cut the waste in half. The 2nd membrane will see slightly higher TDS but will still be in spec unless your source water is over 800 TDS. A 2nd membrane and housing can be added to any RO/DI unit for $60-$100 total.
Might be worth mentioning but as previously mentioned the membranes are designed to run at 4:1 waste ratio. Some people sell units at 2:1 or 3:1 and claim they are more efficient, etc. All they are doing is using a more restrictive resistor and running the membrane out of spec which greatly shortens the life of the membrane. With that said you can do this (I do) BUT you should not run the RO/DI unit in automatic mode with a float switch. You should run it manually and do a manual flush (flush kit) every 25 gallons or so for 15-20 seconds to clean the membrane. It's also a great idea to flush the membrane at the end of the run every time you use it so no junk sits on the membrane and hardens. Of course you can't control this with a float switch as the unit can turn on/off at will.
All the typical "flush kit" is a "Y" in the waste line with a valve on one side and the restrictor on the other side. Both sides then combine back via another "Y" connector. In production mode the one side is closed forcing all water to go through the restrictor. When you open the other side you eliminate the back pressure on the membrane and allow all the junk to flow by instead of through it which cleans it off. This is something you can build yourself from a few parts at HD/Lowes for $6-$10.
I myself use a smaller flow restrictor (more back pressure) with two 150 gpd membranes in series as mentioned above and manually flush the membrane every 20-25 gallons or so. My overall ratio is close to 1.5:1 which I'm happy with. I have 2 more membranes and housings I could install which would easily get me under 1:1 with 600 gpd production BUT then I wouldn't be running the unit every 3 days or so which is bad overall. So I've got the system sized appropriate for membrane life. This IMHO is where people mess up and think a bigger/higher flow system is better. A 50gpd or even 30gpd system is probably size correctly for the average person with a 125g or less system assuming you have room to keep a salt mix container and a pure RO/DI water container. This way you can have one container pre-mixed and ready to go with one container full of fresh water that could be mixed up in an emergency. With the common 44g brute trash cans you could have 80-85 gallons of water always available.
Just some food for thought,
Carlo
I have both a Kent Marine Hi-S Maxima unit and a unit from Filter Direct. The both work well, but it is all about the Membrane. I put a Hi-S membrane in the Filter Direct unit and it makes the world of different. Filmtec is the most well known for Reef use. I am not sure who makes Kent's Hi-S membrane, but blows the doors of the Filmtec for performance and life expectancy (asuming the same water loads and cleaning procedures)
Hi-S
Input Water - 240
Post Membrane - 1
Post DI - 0
Filmtec
Input water - 240
Post Membrane - 6
Post DI - 0
My DI lasts for a long time on my Hi-S maximma.
Hi-S
Input Water - 240
Post Membrane - 1
Post DI - 0
Filmtec
Input water - 240
Post Membrane - 6
Post DI - 0
My DI lasts for a long time on my Hi-S maximma.
Kent sources it's membranes from multiple parties including Filmtec and GE. They are rated at 92 nominal to 96 max rejection rates where Filmtec are rated 96/98 with the exception of the 100gpd membrane which you should never purchase for reef use! They of course rate the entire RO/DI unit as 99.9% since what the RO doesn't do the DI will. However I'm sure most of the membranes are much better then the nominal rating because Filmtec & GE don't really make membranes that low with the exception of the 100 gpd model that I'm aware of. You picked up the silica model which has tighter "pores". They have better rejection rates in the beginning but get worse at a faster rate then "normal" membranes as they clogs up. This is pretty much true of any "S" membrane.
If you have a good membrane you should see TDS reduced from 240 to 9.6 at 96% rejection and down to 4.8 at 98% rejection. Not saying your wrong but I'd find it really hard to believe any "hobby level" membrane is taking 240 TDS down to 1 TDS regardless of cost or manufacture. That would be something like a 99.6% rejection rate.
Generally speaking the spectrapure membranes are tops since they use only Filmtec and hand test and select membranes that do a nominal rate of 98%. You pay basically twice the amount but get a hand tested membrane that does 98% instead of 96% which can pay for itself in DI resin if you use it a lot.
BTW, to accurately measure rejection rates you have the unit running for at least 5 minutes and then take a sample and use a good Conductivity meter that measures in microSiemens at 77F. Something like a Pinpoint Conductivity meter is low-end but usuable to measure down at this level and does temperature compensation with close to accurate results (good enough for hobby use). Any of the in line TDS meters are no where near close enough and easily off by several TDS points. For example a ZERO could easily still be as high as 10 TDS. They are highly effected by air temp, water temp and by the flow of water. Water and air colder then 77F will show lower then true results. Slower flow then 65 psi will also show lower then true results with these in line meters.
I've got a couple in line on mine just for rough measurements and notice them changing quite a bit if I increase pressure from say 45 psi to 65 psi. Just switching membranes even at the same quality can throw off these type of in line meters so it's best to use them for comparison of the same membrane (IE over the life of the same membrane but not to reliable for comparing one membrane to another (in general).
Knowing your post RO/pre DI TDS is helpful to calculate the life of the DI resin. For example if the resin you use is good for 2000 TDS gallons and you end up with 6 TDS going into the DI you should be able to produce 2000/6 or 333.3 gallons before exhausting the resin.
With all that said, Phil. You could have gotten really, really lucky and got a stellar membrane but I wouldn't count on that for replacements when the time comes. Just curious could you give us an update on the TDS reading after letting it run for 5 minutes in another month?
Carlo
If you have a good membrane you should see TDS reduced from 240 to 9.6 at 96% rejection and down to 4.8 at 98% rejection. Not saying your wrong but I'd find it really hard to believe any "hobby level" membrane is taking 240 TDS down to 1 TDS regardless of cost or manufacture. That would be something like a 99.6% rejection rate.
Generally speaking the spectrapure membranes are tops since they use only Filmtec and hand test and select membranes that do a nominal rate of 98%. You pay basically twice the amount but get a hand tested membrane that does 98% instead of 96% which can pay for itself in DI resin if you use it a lot.
BTW, to accurately measure rejection rates you have the unit running for at least 5 minutes and then take a sample and use a good Conductivity meter that measures in microSiemens at 77F. Something like a Pinpoint Conductivity meter is low-end but usuable to measure down at this level and does temperature compensation with close to accurate results (good enough for hobby use). Any of the in line TDS meters are no where near close enough and easily off by several TDS points. For example a ZERO could easily still be as high as 10 TDS. They are highly effected by air temp, water temp and by the flow of water. Water and air colder then 77F will show lower then true results. Slower flow then 65 psi will also show lower then true results with these in line meters.
I've got a couple in line on mine just for rough measurements and notice them changing quite a bit if I increase pressure from say 45 psi to 65 psi. Just switching membranes even at the same quality can throw off these type of in line meters so it's best to use them for comparison of the same membrane (IE over the life of the same membrane but not to reliable for comparing one membrane to another (in general).
Knowing your post RO/pre DI TDS is helpful to calculate the life of the DI resin. For example if the resin you use is good for 2000 TDS gallons and you end up with 6 TDS going into the DI you should be able to produce 2000/6 or 333.3 gallons before exhausting the resin.
With all that said, Phil. You could have gotten really, really lucky and got a stellar membrane but I wouldn't count on that for replacements when the time comes. Just curious could you give us an update on the TDS reading after letting it run for 5 minutes in another month?
Carlo
Carlo said:
I am sure most of us are aware that the inline dm1 and dm2 units are not totally accurate, but used in term of a reference TDS they are fine. I am not looking for an exact number, I am looking for relative change. So if I am getting 1 or 2 post membrane, then see it jump to 5 or 6, then I know something has to be done.
FWIW, I never take a reading until after running for 10 minutes then I check again in 2 or 3 hours. One reason why the numbers are better is that I am using a 35 GPD unit with appropriate flow restrictor, so there us much more membrance contact time. Its not luck, it is consistancy. This is my 3rd membrane between the 2 units, and I have always seen 98%. I need the Silicia removal function (especially when I lived in Deptford)
Yea, that's a perfect use of the in line TDS meters.
Phil, I didn't realize you lived in Deptford. I just moved from there back in March. I remember you living in Turnersville back in the BBS days when I lived in Bridgeton. Deptford had some bad water (reef wise) for a city but overall the TDS wasn't that high (where I lived). Other junk besides dissolved solids in the water.
Anyway, just curious how your getting such high rejection rates. Do you have any idea what the water temperature is going into the unit? Any idea what your pressure is? Do you happen to know if the water is softened before it hits the RO/DI unit?
I ask those question because they are all key to performance testing of membranes. For example most test at 77F at 65 psi with softened water and then quote the spec of the membrane. Under these "ideal" conditions they typically arrive at a value between 96 and 98%. The restritor itself won't really affect the TDS removal to a large degree but may some, but will affect the cleaning of the membrane and it's overall life span. Do you happen to manually flush out your membrane?
Oh another question for you. Are you measuring this just across the membrane pre and post or is the "pre" inline TDS meter before the sediment or carbon filter block? Honestly it's not going to make a great difference but I'm wondering.
If you got some free time to try something for me I'd love to see the results with your TDS meter. Fill a glass with tap water. Then fill a glass with RO water (not DI). Warm both glasses up to 77F (can float them in the sump). Pull one of the TDS meter probes out of the RO/DI unit and use the same one in each glass to get a reading. Using the same probe with the whole probe sunk in the 77F degree water (or pretty close) should give a little better measurement. The air will have less effect on the reading because the probe is sunk in the water.
I'd love to see that if you get the time. I wonder if it will still test at 1 tds or maybe show around 2 or 3 tds (still a darn good rate).
100-(1/240*100)=99.58
100-(2/240*100)=99.16
100-(3/240*100)=98.75
100-(4/240*100)=98.33
100-(5/240*100)=97.91
Just looking at the rates with different TDS values a proper spec membrane would be putting out 4 or 5 TDS after the membrane with 240 as the starting number (98%).
BTW, I wasn't challenging consistency of the membranes at 98%. That can be pretty common. I was just saying don't get used to or expect to always get a new one performing at 99.58% which is staggering. It may not sound like much but the difference between 98 and 99.58% is huge in membranes and DI resin costs. Looking at the little grid/chart/math thing above a 98% rejection membrane would allow about 5 TDS into the DI resin versus the 1 TDS at 99.58%. That means the DI resin would last 5 times longer.
Curious on one other thing if you get time. While the unit is running try timing how long it takes to fill a given quantity of water (any size) from both the waste line and good water line. We can see what the unit is running for it's waste ratio.
Carlo
Phil, I didn't realize you lived in Deptford. I just moved from there back in March. I remember you living in Turnersville back in the BBS days when I lived in Bridgeton. Deptford had some bad water (reef wise) for a city but overall the TDS wasn't that high (where I lived). Other junk besides dissolved solids in the water.
Anyway, just curious how your getting such high rejection rates. Do you have any idea what the water temperature is going into the unit? Any idea what your pressure is? Do you happen to know if the water is softened before it hits the RO/DI unit?
I ask those question because they are all key to performance testing of membranes. For example most test at 77F at 65 psi with softened water and then quote the spec of the membrane. Under these "ideal" conditions they typically arrive at a value between 96 and 98%. The restritor itself won't really affect the TDS removal to a large degree but may some, but will affect the cleaning of the membrane and it's overall life span. Do you happen to manually flush out your membrane?
Oh another question for you. Are you measuring this just across the membrane pre and post or is the "pre" inline TDS meter before the sediment or carbon filter block? Honestly it's not going to make a great difference but I'm wondering.
If you got some free time to try something for me I'd love to see the results with your TDS meter. Fill a glass with tap water. Then fill a glass with RO water (not DI). Warm both glasses up to 77F (can float them in the sump). Pull one of the TDS meter probes out of the RO/DI unit and use the same one in each glass to get a reading. Using the same probe with the whole probe sunk in the 77F degree water (or pretty close) should give a little better measurement. The air will have less effect on the reading because the probe is sunk in the water.
I'd love to see that if you get the time. I wonder if it will still test at 1 tds or maybe show around 2 or 3 tds (still a darn good rate).
100-(1/240*100)=99.58
100-(2/240*100)=99.16
100-(3/240*100)=98.75
100-(4/240*100)=98.33
100-(5/240*100)=97.91
Just looking at the rates with different TDS values a proper spec membrane would be putting out 4 or 5 TDS after the membrane with 240 as the starting number (98%).
BTW, I wasn't challenging consistency of the membranes at 98%. That can be pretty common. I was just saying don't get used to or expect to always get a new one performing at 99.58% which is staggering. It may not sound like much but the difference between 98 and 99.58% is huge in membranes and DI resin costs. Looking at the little grid/chart/math thing above a 98% rejection membrane would allow about 5 TDS into the DI resin versus the 1 TDS at 99.58%. That means the DI resin would last 5 times longer.
Curious on one other thing if you get time. While the unit is running try timing how long it takes to fill a given quantity of water (any size) from both the waste line and good water line. We can see what the unit is running for it's waste ratio.
Carlo
I attribute the good rejection rate to SLOW flow in that unlike you guys with 75/100 membranes, there is more water contact time. I am also using .5 micron filter and .5 micron carbon blocks
I have a DM1 and DM2 inline, Dm1 is raw water in, and post membrane, Dm2 is post membrane and post DI. The combo of DM1 and Dm2 at the post membrane stage are never different by more that 1 tds, usually showing 1 or 2.
My water comes in at high pressure 70 PSI, but colder that spec. The units are never left to run or turn on and off via float valves. The are deliberately turned on and off via the source water into Brute cans that have float values to trigger when to flow from a barrel to the other.
In reality, its not going to matter one way or another 1% or 2% here or there. I think generally in the hobby we spend way to much time on the exact numbers and stress my Ph is not exactly xxxxx, my temp gauge isoff .3 degrees. Just use your eyes, does it look good, is everyone happy in the tank, assuming people actually spend time looking at their tanks.
I have a DM1 and DM2 inline, Dm1 is raw water in, and post membrane, Dm2 is post membrane and post DI. The combo of DM1 and Dm2 at the post membrane stage are never different by more that 1 tds, usually showing 1 or 2.
My water comes in at high pressure 70 PSI, but colder that spec. The units are never left to run or turn on and off via float valves. The are deliberately turned on and off via the source water into Brute cans that have float values to trigger when to flow from a barrel to the other.
In reality, its not going to matter one way or another 1% or 2% here or there. I think generally in the hobby we spend way to much time on the exact numbers and stress my Ph is not exactly xxxxx, my temp gauge isoff .3 degrees. Just use your eyes, does it look good, is everyone happy in the tank, assuming people actually spend time looking at their tanks.
Wow! All this stuff is way over my head . I think im going to get an Air Water Ice 75gpd 5 stage.
. I think im going to get an Air Water Ice 75gpd 5 stage.ocmsolidsnake said:Wow! All this stuff is way over my head
LOL I hear ya!... here's the link to make it simply just as good as AWI go with whatever saves you the most money http://cgi.ebay.com/AQUARIUM-2-110G...hZ002QQcategoryZ20756QQtcZphotoQQcmdZViewItem
Just ask them to change the membrane to a 75GPD (they wont charge for it)
I agree with you Phil on using your eyes and viewing the tank for sure. Much information can be gained from doing this.
Cold water and 70 psi will definitely help a lot. The cold water causes the pores of the membrane to shrink but the very, very good water pressure still makes sure the water gets pushed through the membrane.
I have a question about the comment:
"I have a DM1 and DM2 in line, Dm1 is raw water in, and post membrane, Dm2 is post membrane and post DI. The combo of DM1 and Dm2 at the post membrane stage are never different by more that 1 TDS, usually showing 1 or 2."
Is DM1 pre or post membrane? It sounds like before the unit itself (raw) but then you say "post" (after) membrane. I'm guessing that's a typo and you meant "pre" correct?
"Dm2 is post membrane and post DI". Are you saying the last meter is after the DI stage? If it isn't between the membrane and the DI stage then I'd expect the result to come back at 0 or 1 TDS as you had mentioned since it's running thought the DI before getting measured.
What I was talking about membrane rejection wise it the measurement directly before and directly after the membrane. So 1st meter is between the carbon block and the membrane and the second is between the membrane and the DI filter. If they aren't in these exact spots you really can't calculate the rejection rate of the membrane. Of course this assumes the person cares about this and obviously many people will not and just care what the start and end products are.
I'm anal and like to know how each part of my system works so I can improve upon it when the time comes. I like to run 2 of the in line units on the RO/DI system since the meters are cheap. I like the following setup:
TDS meter
sediment filter
carbon block
TDS meter
membrane
TDS meter
DI
TDS meter
With this type of configuration you can see the starting TDS and ending TDS and see the pre and post membrane performance. It's easy to see when the membrane has dropped off a little bit performance wise (gain of a couple TDS points from usual) and you can manually flush it and give it a good cleaning.
Carlo
Cold water and 70 psi will definitely help a lot. The cold water causes the pores of the membrane to shrink but the very, very good water pressure still makes sure the water gets pushed through the membrane.
I have a question about the comment:
"I have a DM1 and DM2 in line, Dm1 is raw water in, and post membrane, Dm2 is post membrane and post DI. The combo of DM1 and Dm2 at the post membrane stage are never different by more that 1 TDS, usually showing 1 or 2."
Is DM1 pre or post membrane? It sounds like before the unit itself (raw) but then you say "post" (after) membrane. I'm guessing that's a typo and you meant "pre" correct?
"Dm2 is post membrane and post DI". Are you saying the last meter is after the DI stage? If it isn't between the membrane and the DI stage then I'd expect the result to come back at 0 or 1 TDS as you had mentioned since it's running thought the DI before getting measured.
What I was talking about membrane rejection wise it the measurement directly before and directly after the membrane. So 1st meter is between the carbon block and the membrane and the second is between the membrane and the DI filter. If they aren't in these exact spots you really can't calculate the rejection rate of the membrane. Of course this assumes the person cares about this and obviously many people will not and just care what the start and end products are.
I'm anal and like to know how each part of my system works so I can improve upon it when the time comes. I like to run 2 of the in line units on the RO/DI system since the meters are cheap. I like the following setup:
TDS meter
sediment filter
carbon block
TDS meter
membrane
TDS meter
DI
TDS meter
With this type of configuration you can see the starting TDS and ending TDS and see the pre and post membrane performance. It's easy to see when the membrane has dropped off a little bit performance wise (gain of a couple TDS points from usual) and you can manually flush it and give it a good cleaning.
Carlo
Carlo said:
Mine is..
TDS meter DM1 (Normally 240TDS)
sediment filter .5 micron
carbon block .5 micron
membrane (Hi-S silica membrane, Kent Marine)
TDS meter DM1 (Normally 1 TDS)
TDS meter DM2 (Normally 2 or 3)
DI
TDS meter DM2 (Normally 0 TDS)
The reason I have 2 meters on postpmembrane is how many times have people run a test on something and you just don't belive the results, so you suspect your test kit. The you get a 2nd or 3rd and have to play the "which is right game". Since I am not looking at EXACT numbers, but relative numbers, this resolves the issue. When both DM1 and DM2 increase by the same amount I have to do something. The blocks are the cheap part, its not that important to know at EXACTLY which point I ahve to make a change, I just want to TRUST that a change has to happen.
So back to the ORIGINAL POINT OF THIS THREAD. I really makes no difference on how much you pay for the RODI system as far as quality goes. Its about the parts inside it (membrane, filters, etc). My original comment was to show that a lower end $100 unit works as good as the $275 just by changing the membrane.