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

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Chrisv.

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About 2 years ago, I won a new RODI unit from Bulk Reef Supply at a raffle through my local reef club (shout out Boston reefers!). I haven't had the space to install it until now. The unit comes with a pre-installed DI canister that's not packaged in foil of any kind, but is already in the housing.

I set it all up and my source TDS is 75, my post-RO TDS is 5, and my post DI TDS is 2-3. I'm wondering if the mixed bed resin has expired. When I measure TDS using an (admittedly super cheap) TDS meter, the TDS shows as zero. When I use the in line TDS meter that came with the unit, the TDS is 2-3.

I'm happy to replace the DI resin if needed, but I am left wondering if it's the DI resin that's bad, or a false positive from the in line TDS meter.

What do you guys think?
 
Tidal Gardens
Resin can last years if in a sealed bag, my guess is the resin containers are not enough and you need new.
 
I would buy new resin, but also make sure to get a mixed resin, not a cation-only or anion-only resin. Not sure what BRS RO/DI units use out of the box, but many brands come with cation-only resin. If you're having trouble cleaning up those last few ppm, having the anion component along with the cation component in mixed resin may help.

Another thing is sometimes RO/DI units need a little break in time to get the membrane fully hydrated. Maybe try testing again after running a good 30-50 gallons through it.
 
Just double checking, did you let it run for an hour or so and then check it?

With all new filters it’s good to let it run for a little the first time
 
Chrisv. said:
I'm happy to replace the DI resin if needed, but I am left wondering if it's the DI resin that's bad, or a false positive from the in line TDS meter.
Click to expand...
Impossible to know the answer without
A. a third tds meter, or
B. replacing the resin and testing again.
 
As others stated, make sure it has run for awhile before doing any testing. With new filters I usually make 3 to 5 gallons of good water before doing any testing. If the DI was dry then there it could be bad. Many state that you shouldn't use dry DI but I've done it before with no issues.

I would be more worried about your RO membrane. If the tap tds is really 75 and you are getting 5 after the ro membrane then you are the lowest end of the membrane efficiency. I would expect to see 1 tds after the membrane. My tap tds is over 400 and my tds after the membrane is 5 or 6.
 
Chrisv. said:
About 2 years ago, I won a new RODI unit from Bulk Reef Supply at a raffle through my local reef club (shout out Boston reefers!). I haven't had the space to install it until now. The unit comes with a pre-installed DI canister that's not packaged in foil of any kind, but is already in the housing.

I set it all up and my source TDS is 75, my post-RO TDS is 5, and my post DI TDS is 2-3. I'm wondering if the mixed bed resin has expired. When I measure TDS using an (admittedly super cheap) TDS meter, the TDS shows as zero. When I use the in line TDS meter that came with the unit, the TDS is 2-3.

I'm happy to replace the DI resin if needed, but I am left wondering if it's the DI resin that's bad, or a false positive from the in line TDS meter.

What do you guys think?
Click to expand...
I think you should have them replaced.
 
Randy Holmes-Farley said:
Does that meter ever read zero? Its probably a test error.
Click to expand...
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?
 
Chrisv. said:
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?
Click to expand...

As for the meter, you can easily pull it out and make sure it is oriented correctly. You want the water running through them. Like field goal posts
 
Chrisv. said:
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?
Click to expand...

Did you check to see if they were correct?

How much water did you pass thru the resin?

1725818112731.png
 
Top Shelf Aquatics
Chrisv. said:
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?
Click to expand...
Once wetted, an RO MEMBRANE needs to stay wet. The same does not apply to ion exchange resin. Your challenge with storing resin is to not expose it to air. Common plastic bags do not work as they allow vapor to pass through.
 
Buckeye Hydro said:
Once wetted, an RO MEMBRANE needs to stay wet. The same does not apply to ion exchange resin. Your challenge with storing resin is to not expose it to air. Common plastic bags do not work as they allow vapor to pass through.
Click to expand...
Can I store the di resin in a sealed bag or other container of water?
 

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