High TDS and DI Resin Longevity

[nightOwl]

Hi all am wondering if there is an expected time DI resin should last based on the TDS readings. I live in MD and apparently the water is really bad or my RODI unit is is not enough. I have a 300 GPD unit that I just switched out all the filters, membranes, added a second resin chamber, and added new resin. This was done 3 days ago and already my stage one sediment filter is showing signs that is it browning. The first DI resin chamber is also starting to turn brown at the bottom. My TDS readings were 219 today on the raw water side. I am getting 0 TDS after my second DI resin so the water appears to have been processed fine. My concern is that at this rate I am going to need my own DI resin factory and filter factory to keep my water clean. It has only been three days and I have flushed the membranes for about 5 minutes before and after making water. My set up also includes a booster pump not sure if that will make a difference but I thought I would mention it. Is there anything I can do or change or is the high TDS readings going to make me burn through filters and DI resin really fast?


10/13/2017
IMG_9742 by LifeThrough_TheLense, on Flickr


219 TDS
IMG_9744 by LifeThrough_TheLense, on Flickr

10/16/2017
IMG_9750 by LifeThrough_TheLense, on Flickr

IMG_9751 by LifeThrough_TheLense, on Flickr

 

[Potatohead]

You need to check two things;

1) the actual water pressure going into the membrane
2) The TDS between the membrane and DI

Also, do you have a flush valve installed?

 

[nightOwl]

You need to check two things;

1) the actual water pressure going into the membrane
2) The TDS between the membrane and DI

Also, do you have a flush valve installed?

Potatohead - Would I need to change where the pressure gauge is currently connected?

Should I expect the reading between the membrane and the DI to read zero?

I have a flush value installed on the unit.

 

[Potatohead]

OK I should have paid more attention to the pics. If that is the stock gauge on the unit, it's already between the carbon and membrane as it should be. What is does it read with the pump on?

It will likely not read zero TDS after membrane, but it should be rejecting at least 95%, hopefully more like 98%. So you should be reading about 5-10 TDS after membrane. This is largely dependent on the pressure.

 

[mcgyvr]

Potatohead - Would I need to change where the pressure gauge is currently connected?

Should I expect the reading between the membrane and the DI to read zero?

I have a flush value installed on the unit.

The TDS before the DI and right after the RO should be 90whatever % less than supply TDS (rejection ratio of the membrane)..many are usually 93-99% depending on brand.. so like 8-10 TDS or so..

Your membrane might not be seated properly or something allowing full TDS through it..

 

[nightOwl]

You need to check two things;

1) the actual water pressure going into the membrane
2) The TDS between the membrane and DI

Also, do you have a flush valve installed?

OK I should have paid more attention to the pics. If that is the stock gauge on the unit, it's already between the carbon and membrane as it should be. What is does it read with the pump on?

It will likely not read zero TDS after membrane, but it should be rejecting at least 95%, hopefully more like 98%. So you should be reading about 5-10 TDS after membrane. This is largely dependent on the pressure.

Potatohead - With the pump on the pressure is reading about 95 and the reading coming from after the membrane was around 15-20 but I will have to take things apart to the get the exact measurement after the membrane.

 

[nightOwl]

The TDS before the DI and right after the RO should be 90whatever % less than supply TDS (rejection ratio of the membrane)..many are usually 93-99% depending on brand.. so like 8-10 TDS or so..

Your membrane might not be seated properly or something allowing full TDS through it..

mcgyvr - I think they are seated properly. When I did not have them fully engaged the canister would close. Also I may have forgotten but sometimes my incoming TDS readings are upwards of 240.

 

[Potatohead]

Potatohead - With the pump on the pressure is reading about 95 and the reading coming from after the membrane was around 15-20 but I will have to take things apart to the get the exact measurement after the membrane.

If your flush valve is installed between the DI and membrane you can just open it, let it run for a few minutes and then see where the TDS bottoms out.

Assuming those three membranes in the pic mean you have three 100 gpd membranes in series, I don't know how much more you can do. You have much less waste water with this type of setup but you will always have more TDS going into your DI because you are feeding waste from one into the next, and then doing it again. If you plumb them in series you will have more waste water but you will also use less DI resin. However if you want to change to parallel plumbing I would probably ask AquaFX their recommendation because you will likely need to change/modify your flow restrictor and you may need larger inlet/outlet hoses.

Edit - Also, are those DOW 100 gpd's or are they the AquaFX ones? Unfortunately the DOW 100's are not very good, they only have a 90% rejection rate.

 

[Opus123]

As long as you don't see a drop in pressure, I wouldn't worry about the color of the sediment filter. As for you water, I would love to see 240 tds, mine is close to 500. I get 4 tds after my spectrapure RO membrane. If you are getting 20 tds after your RO membrane then your DI canister will last for around 220 gallons. I don't trust the color changing in the DI resins. Mine will change color but still give me 0 tds for many months.

 

[nightOwl]

The TDS before the DI and right after the RO should be 90whatever % less than supply TDS (rejection ratio of the membrane)..many are usually 93-99% depending on brand.. so like 8-10 TDS or so..

Your membrane might not be seated properly or something allowing full TDS through it..

If your flush valve is installed between the DI and membrane you can just open it, let it run for a few minutes and then see where the TDS bottoms out.

Assuming those three membranes in the pic mean you have three 100 gpd membranes in series, I don't know how much more you can do. You have much less waste water with this type of setup but you will always have more TDS going into your DI because you are feeding waste from one into the next, and then doing it again. If you plumb them in series you will have more waste water but you will also use less DI resin. However if you want to change to parallel plumbing I would probably ask AquaFX their recommendation because you will likely need to change/modify your flow restrictor and you may need larger inlet/outlet hoses.

Edit - Also, are those DOW 100 gpd's or are they the AquaFX ones? Unfortunately the DOW 100's are not very good, they only have a 90% rejection rate.

Potatohead - Thanks again for you help. The membranes are the DOW 100 but for some reason I thought they were 96% rejection rating. I guess the set up is optimal for what I am doing. I will just keep an eye on the TDS measuement and once it starts to rise just replace the filters.

As long as you don't see a drop in pressure, I wouldn't worry about the color of the sediment filter. As for you water, I would love to see 240 tds, mine is close to 500. I get 4 tds after my spectrapure RO membrane. If you are getting 20 tds after your RO membrane then your DI canister will last for around 220 gallons. I don't trust the color changing in the DI resins. Mine will change color but still give me 0 tds for many months.

Opus123 - Thanks for the input. I was thinking my water was the worse now I don't feel so bad...lol. I will check the TDS reading tomorrow after the membranes and see what it is.

 

[Potatohead]

If it's around 20 after membranes that's not too bad. Typically after one membrane your waste water will be about 50% more TDS than the tap. So you are then feeding like 330 into the next membrane and then about 500 into the third one. So if you are at 20 that's about 96% rejection

 

[Buckeye Hydro]

Unfortunately the DOW 100's are not very good, they only have a 90% rejection rate.

This hasn't been the case in years. The current Filmtec 100 gpd's are rated at 98%

 

[nightOwl]

If it's around 20 after membranes that's not too bad. Typically after one membrane your waste water will be about 50% more TDS than the tap. So you are then feeding like 330 into the next membrane and then about 500 into the third one. So if you are at 20 that's about 96% rejection

Potatohead - I think you are right and everything is working fine now.

This hasn't been the case in years. The current Filmtec 100 gpd's are rated at 98%

Buckeye Hydro - Thanks for also clarifying this.