RO/DI - Are all equal?

attilak

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Hi,

I am debating on changing out my 6 stage fountainhead RODI system, but before I do I wanted to ask a simple question. Are all RO/DI system pretty much made the same? it maybe a dumb question, but it seems that I have to continuously replace the Deionization Resin (Color Changing) media after say 200 gal of RODI produced. My TDS goes from 0 to 10 within a week after making about 200 gal, so try to flush out and maybe get another 50 gal out of it - then I have to change media. I also change all other filter media every month. I just want to know if this is normal or should be looking at another RODI system.

Thanks,
Attila
 
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Montiman

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Any quality 4 stage system will provide you with 0TDS water but the questions is at what cost. Some will need filter replacements far more frequently than others and some systems produce far more waste water than others. In your situation you are replacing media far more frequently than I would consider reasonable so I would start by confirming when each filter needs to be replaced.

Sediment filters only need to be replaced when the pressure gauge on the membrane shows a drop in pressure. If you don't have a pressure gauge then get one they cost about as much as one or two filters.

Carbon blocks only need to be replaced when chlorine breaks through to the membrane. You can test the chlorine concentration of your waste water to confirm that the carbon block removed all the chlorine. Buy a chlorine test at a pool supply store and if any chlorine shows replace the block.

Membranes should last for multiple years. The only way to know if your membrane is performing is to use a TDS meter. I like a dual meter with one sensor reading the input water and one reading the after membrane water. Once you see membrane rejection drop below around 95% replace the membrane.

DI should be replaced as exhausted. Either use color changing resign or a TDS meter. If your resign changes color or the TDS meter reads above 0 then replace the resign.

I believe you are replacing your pre-filters before you need to or there is something else hurting your system performance. Here is a series of questions to help us find out how to get better efficiency.

What is the TDS Pre and Post membrane?
What DI resign are you using?
What is the pressure entering the membrane?
 

Water Dog

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A few questions...

What is your water pressure?
Are you on city water or well water?
What is the TDS of your water from the tap and after the RO membrane?
 
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SliceGolfer

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I have a 7 stage 75 gpd BRS unit with separate DI resins. Super handy to swap just the expired resin based on color change material.

Maybe add the separate DI cartridges to your existing unit?
 

pdxmonkeyboy

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If you are going through DI resin that fast it may be better to just buy a three stage resin filter instead of a new rodi unit.

You may have something in your water exhausting your resin. Normal resin is a mixture of anion and cation resin. You are exhausting all of one part of the two part. A three stage di has a canister of anion, then a canister of cation then a canister of mixed resin.

That way you can replace just the one that is getting exhausted. I had to do this and works well..
 

jjstecchino

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Hi,

I am debating on changing out my 6 stage fountainhead RODI system, but before I do I wanted to ask a simple question. Are all RO/DI system pretty much made the same? it maybe a dumb question, but it seems that I have to continuously replace the Deionization Resin (Color Changing) media after say 200 gal of RODI produced. My TDS goes from 0 to 10 within a week after making about 200 gal, so try to flush out and maybe get another 50 gal out of it - then I have to change media. I also change all other filter media every month. I just want to know if this is normal or should be looking at another RODI system.

Thanks,
Attila
Needing to change the DI resin after 200G of RO water is definitely not normal.
RO/DI system are pretty straightforward. The brand of the canisters doesn't really matter and everything is in the filters.
If I were you I would try to troubleshoot the system you already own rather than looking at a replacement. You may need to get new filters/membrane though.
Make sure your water travels from the tap to a sediment filter (it looks like dense felt) then to one or two stages of carbon filters. Then water will go to the membrane housing. Make sure it is properly connected and that you are not sending your waste water to the DI canister. Refer to the image below and double check yours.

$_57.PNG


Water goes then from the pure water outlet of the housing to your DI canister.

For the membrane to work you need appropriate pressure at the water feed (60+ psi) and a flow restrictor at the waste water outlet. Each membrane has a recommended restrictor depending on brand/gallon per day rating. Check with the manufacturer of your membrane. If you need a shortcut, look at BRS RO/DI systems and buy a complement of filters/membrane/restrictor just like one of their systems. They work well and efficiently.

Once everything is square, you should have almost 0 TDI at the membrane pure water outlet and the resin should last for many months.
 

Water Dog

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Based on what came up in a search for a Fountainhead 6 stage RODI unit, I would say no, you do not need to buy a new unit. A good start would be to add a pressure gauge, a triple inline TDS meter so you can monitor tap, post RO and post DI resin TDS and a 3 way valve for DI bypass.


But we do need to find out the underlying cause for why you’re ripping through resin so fast. See my questions above so we can start diagnosing the issue.
 
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attilak

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Hi, thanks for the quick responses! Montiman - very good info on Sediment filter replacements, as I had no idea about looking at pressure dropping and replace only then ... right now I have a pressure showing about 55 psi, which is directly connected right at the inbound of the RODI filter (see pic). I do have a TDS meter, actually purchased one with 3 probes, right now I only have the IN and OUT, but need to put a probe right at the exit of the membrane.

What is the TDS Pre and Post membrane? its 88 entering unit and now it is 0 out - but just changed DI resin.
What DI resign are you using? I purchase the one from bulk reef supply. https://www.bulkreefsupply.com/brs-bulk-deionization-resin-color-changing.html
What is the pressure entering the membrane? looks to be around 55 psi. this is the pressure entering the unit. should I get another pressure guage and install right before membrane?
Are you on city water or well water? I am using city water.

20191106_111555.jpg 20191106_111619.jpg 20191106_111624.jpg
 
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Water Dog

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Thanks for the pictures... for starters, get rid of the horizontal DI cylinders. They are prone to channeling and are not very efficient. Second, you mentioned that after a week of making water, TDS out of the DI stage goes up to 10. If your incoming TDS is 88 and after your DI is spent and it comes out as 10, that tells me you’re getting an 89% rejection rate from your membrane.
 
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lpsouth1978

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Get that last probe installed post membrane and let us know what the reading is. If the TDS post membrane is low and the resin is exhausting quickly, it could be CO2 in the water. It could also be that there is something in the water that is exhausting one of the resins too fast. A triple canister DI resin with Anion, Cation, and mixed will usually fix this. Typically one of the resins will become exhausted and the others will last a very long time.
 
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attilak

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Based on what came up in a search for a Fountainhead 6 stage RODI unit, I would say no, you do not need to buy a new unit. A good start would be to add a pressure gauge, a triple inline TDS meter so you can monitor tap, post RO and post DI resin TDS and a 3 way valve for DI bypass.


But we do need to find out the underlying cause for why you’re ripping through resin so fast. See my questions above so we can start diagnosing the issue.
Thanks... yup, this is exactly the one I purchased. Glad you're saying I may not need a new unit as my basement is starting to look like a commercial water treatment plant :) with all of this equipment I am adding onto my system. Honestly, another concern I have is dealing with high phosphates, which is another reason I am looking at this and seeing if it is a source of one of my problems.

So, you can see from the pics - I have a pressure gauge right at the pre-filter - entering unit. I purchased 3 probe TDS meter as well. I do not understand the 3 way valve bypass though ... maybe I will take pics of the unit and make sure it is correctly connected. I think if it was incorrect though, I would think that my TDS would not be 0.
 
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attilak

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Thanks for the pictures... for starters, get rid of the horizontal DI cylinders. They are prone to channeling and are not very efficient. Second, you mentioned that after a week of making water, TGD out of the DI stage goes up to 10. If your incoming TDS is 88 and after your DI is spent and it comes out as 10, that tells me you’re getting an 89% rejection rate from your membrane.
When you say get rid of the horizontal DI canisters. are you suggesting I buy a different RODI system? I am not familiar with RODI systems, and maybe I can just replace the DI resin canister with different ones.
 
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attilak

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Get that last probe installed post membrane and let us know what the reading is. If the TDS post membrane is low and the resin is exhausting quickly, it could be CO2 in the water. It could also be that there is something in the water that is exhausting one of the resins too fast. A triple canister DI resin with Anion, Cation, and mixed will usually fix this. Typically one of the resins will become exhausted and the others will last a very long time.
Thanks. Yes, I will install that last probe and let you know what the reading is ... no problem. I will do this in the evening today and re-post result.
 
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jjstecchino

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Thanks... yup, this is exactly the one I purchased. Glad you're saying I may not need a new unit as my basement is starting to look like a commercial water treatment plant :) with all of this equipment I am adding onto my system. Honestly, another concern I have is dealing with high phosphates, which is another reason I am looking at this and seeing if it is a source of one of my problems.

So, you can see from the pics - I have a pressure gauge right at the pre-filter - entering unit. I purchased 3 probe TDS meter as well. I do not understand the 3 way valve bypass though ... maybe I will take pics of the unit and make sure it is correctly connected. I think if it was incorrect though, I would think that my TDS would not be 0.
Did you measure your TDS just after the membrane and before the DI? It could be 0 after the DI but very high before and this may be the reason you are running through resin so fast. If you measure before and after the membrane you can calculate your rejection rate and see if it is what is expected from the membrane. If it is not it may be a bad membrane or inappropriate restrictor. Your water pressure could be better but it is not a show stopper.

Would double check connections at the membrane outlets as well. I think you may be pumping extremely high TDS through your DI
 

Water Dog

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I would replace the membrane with a 75gpd Dow Filmtec 98% rejection rate membrane.


I would put your pressure gauge right before the membrane so you will notice pressure drops over time from when prefilters are brand new.

I would then put the TDS sensors before and after the RO membrane and then after the DI stages.

I would add a 3 way valve to bypass the DI stage upon startup so TDS creep water won’t burn up your DI resin


Then I would replace the horizontal DI cylinders with this dual stage DI kit. These allow for efficient use of your DI resin without the inefficient channeling that occurs when using horizontal DI cylinders.


Then put the third TDS probe sensor post the DI canisters.
 
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