RODI expired, TDS= 2...whats up?

[Randy Holmes-Farley Verified Community Expert]

Well it's a new unit, so I have no clue. It's designed to read zero, but I agree that while the first DI may have been bad, I have no reason to believe that she second is.

I read online that if the electrodes in a flow through TDS meter are not installed properly, the meter will always read 2 or 3. Apparently they are very orientation specific. I did not install the TDS electrodes, so I'm wondering if that's what's happening here.

In the meantime, if this is true, that means I may very well have an essentially unused di cartridge that is now wet. Any way to keep it and use it when the newly acquired one goes bad?

I don’t understand how orientation causes an issue, but they are very cheaply made for ro/di applications and certainly may have issues.

 

[twentyleagues]

I don’t understand how orientation causes an issue, but they are very cheaply made for ro/di applications and certainly may have issues.

I have wondered that myself. I was told the water needs to be flowing in between the electrodes. I would think that would still happen in either orientation. But not a scientist so I just do what I am told.

 

[Buckeye Hydro Verified Sponsor]

I will pop the line out of the fitting and have a look.

Suggest you do not pop the probe out of the fitting. Once you scratch the probe it may not seal. Simply rotate the probe in the fitting until the notch is oriented as shown above.

 

[Buckeye Hydro Verified Sponsor]

The units are calibrated with the probes aligned perpendicular to the water flow. I've seen many times a difference of several ppm based upon the orientation of the probes.

 

[Bosreef]

Have nothing to add but wanted to shout out boston reefers! Fellow member here!

 

[Randy Holmes-Farley Verified Community Expert]

The units are calibrated with the probes aligned perpendicular to the water flow. I've seen many time a difference of several ppm based upon the orientation of the probes.

Still makes no sense to me unless flow is so fast that there are air gaps in between.

 

[Marcus H.]

Chris

Do you know what actual ions are contributing to your TDS? The 95 to 99% efficiency is just a rule of thumb. My water is high in Sodium and Bicarbonate. RO membranes typically only remove 95 to 96% of bicarbonate and for sodium it can be an even wider band. So in my system I see a 94% reduction coming out of the Ro Unit which is right inline with what I can expect. So I just roll with it The bicarbonate concentration of seawater is around 140 ppm and sodium is orders of magnitude more so in my case who cares.

If you are dealing with phosphates, nitrates, sulfates or some other ion then maybe it is worth it to chase it down.

 

[Chrisv.]

Chris

Do you know what actual ions are contributing to your TDS? The 95 to 99% efficiency is just a rule of thumb. My water is high in Sodium and Bicarbonate. RO membranes typically only remove 95 to 96% of bicarbonate and for sodium it can be an even wider band. So in my system I see a 94% reduction coming out of the Ro Unit which is right inline with what I can expect. So I just roll with it The bicarbonate concentration of seawater is around 140 ppm and sodium is orders of magnitude more so in my case who cares.

If you are dealing with phosphates, nitrates, sulfates or some other ion then maybe it is worth it to chase it down.

I don't. I suppose icp mass spec could be used on the purified water to find out, but I honestly wonder if this isn't just a false positive. I have another (handheld) TDS meter that gives a TDS of zero and this in line TDS meter has given me the 2-3 ppm with old resin and with brand new resin.

Unfortunately I sort of cheaped out on the handheld TDS meter when I bought it many years ago, so it likely isn't very high quality. Then again if you look on Amazon it looks like a they all come from the same factory.

 

[livinlifeinBKK]

Well, I bought some new resin. TDS still equals 2.

If its not a problem with your probe, what you need is an RO Buddie! 0 TDS!

 

[Marcus H.]

I don't. I suppose icp mass spec could be used on the purified water to find out, but I honestly wonder if this isn't just a false positive. I have another (handheld) TDS meter that gives a TDS of zero and this in line TDS meter has given me the 2-3 ppm with old resin and with brand new resin.

Unfortunately I sort of cheaped out on the handheld TDS meter when I bought it many years ago, so it likely isn't very high quality. Then again if you look on Amazon it looks like a they all come from the same factory.

You can send your water in to have it tested. I send mine to Texas A and M Agrilife extension office. The Soil, water, Forage testing Laboratory. I used an irrigation analysis but they have one for aquaculture. I would call and ask. They use both mass spectroscopy and simple titrations. You can also ship it there. It might be a good way to to determine how much time and money you want to throw at this. You could even send the post RO sample. I hope this is helpful.

Soil Testing Lab – Soil, Water and Forage Testing Laboratory

Soil, Water and Forage Testing Laboratory

soiltesting.tamu.edu

 

[Randy Holmes-Farley Verified Community Expert]

You can send your water in to have it tested. I send mine to Texas A and M Agrilife extension office. The Soil, water, Forage testing Laboratory. I used an irrigation analysis but they have one for aquaculture. I would call and ask. They use both mass spectroscopy and simple titrations. You can also ship it there. It might be a good way to to determine how much time and money you want to throw at this. You could even send the post RO sample. I hope this is helpful.

Soil Testing Lab – Soil, Water and Forage Testing Laboratory

Soil, Water and Forage Testing Laboratory

soiltesting.tamu.edu

For a tank sample, I’d be wary of using a method not designed for seawater.

 

[Marcus H.]

Ahh yeah this is just for the RoDI or what is coming out of the tap! if I took seawater in there I would get a funny look for sure!

 

[Righteous]

Do you have a photo of the inline meter and where it’s installed? Maybe it’s not installed after the resin but after the RO? Or is it possible you have more than one TDS meter attached? I have a BRS with 3 seperate inline meters with a readout with a switch.

 

[Chrisv.]

Do you have a photo of the inline meter and where it’s installed? Maybe it’s not installed after the resin but after the RO? Or is it possible you have more than one TDS meter attached? I have a BRS with 3 seperate inline meters with a readout with a switch.

I’ll post a photo tomorrow— unfortunately mine is just the two way unit. I suspect I will need to replace it and when I do I’ll buy the three way.

 

[Buckeye Hydro Verified Sponsor]

I’ll post a photo tomorrow— unfortunately mine is just the two way unit. I suspect I will need to replace it and when I do I’ll buy the three way.

Or just add a single probe meter to supplement what you have

SM1 In-Line Single TDS Meter

At Buckeye Hydro we specialize in providing the highest quality water filtration systems and accessories for every potential need.

www.buckeyehydro.com

 

[Jolson10]

Still makes no sense to me unless flow is so fast that there are air gaps in between.

Air was my issue. I now just force production rate to slow with a ball valve to ensure DI cans stay completely full of water and no air.

 

[Buckeye Hydro Verified Sponsor]

Air was my issue. I now just force production rate to slow with a ball valve to ensure DI cans stay completely full of water and no air.

Hmmm. If I understand correctly what you're doing will apply backpressure on the membrane - not a good thing. How about you just burp your DI housing(s) and don't allow the DI water to siphon out when you're done with production?

 

[Chrisv.]

If anyone is interested in how this story ended, I bought a second of the same hm TDS meters and installed it. With both meters in line I was getting 0 TDS with the new one and 4-5 with the old one. Given that I already replaced the di resin and that it agrees with the results of the handheld meter, I'm calling it zero.

 

[Cichlid Dad]

Air was my issue. I now just force production rate to slow with a ball valve to ensure DI cans stay completely full of water and no air.

If you are taking about the air left in the canister as you are looking at it, first it's fine, the resin in the tube is full of water, second , just turn on the unit and loosen the canister, the air will leak out, then tighten it once the air is gone.