Question about TDS readings?

[jbird0420]

I have a question about TDS readings..?

My rodi unit just had fresh carbon, silica, and sediment filter changes a week ago. Today I replaced the old membrane with the new 50 gpd membrane. It's a Kent rodi Hi-s 60gpd rodi unit.

I used a new TDS meter I purchased. It's reading 860 ppm on product water before membrane change. I changed out the membrane in my rodi unit and replaced with a new membrane. Ran some new product water in a cup, TDS reads 108 ppm. Is that a normal reading?
I thought it should be at 0 ppm??


Thanks for the help!

 

[Randy Holmes-Farley]

Did you run a little water through it before collecting?

Does the meter read 0 ppm TDS in air?

Was the collecting container totally clean? Even traces of previous stuff can boost TDS a lot.

Not sure what you mean by a silica cartridge. You mean the DI? It is after the RO membrane, right?

If the TDS is not zero, then the DI is depleted. If you do not have a DI cartridge, you will not get 0 ppm TDS.

 

[jbird0420]

Thanks for the help. Answers below..

Did you run a little water through it before collecting? No, just collected after membrane change

Does the meter read 0 ppm TDS in air? Yes

Was the collecting container totally clean? Even traces of previous stuff can boost TDS a lot. No, it's a 35g trash can I use for water changes. It had about 20 gallons already made up water, before I switched out the membrane.

Not sure what you mean by a silica cartridge. You mean the DI? It is after the RO membrane, right? Yes, the DI is what I'm referring to. Yes, the DI cartridge is hooked up after the membrane

If the TDS is not zero, then the DI is depleted. If you do not have a DI cartridge, you will not get 0 ppm TDS.

DI is brand new, just changed it and carbon and sediment filters in rodi unit a week ago.

 

[AquaReeferMan]

With all new filters and membrane I would suspect a faulty TDS meter. What kind is it? Was it calibrated?

 

[jbird0420]

New HM digital TDS meter. Just got it yesterday.

With all new filters and membrane I would suspect a faulty TDS meter. What kind is it? Was it calibrated?

 

[jbird0420]

Update! Just took a new reading from product water. TDS reads between 10-12ppm.. I guess the new membrane needs a little time to adjust...? lol

 

[Randy Holmes-Farley]

No, it's a 35g trash can I use for water changes. It had about 20 gallons already made up water, before I switched out the membrane.

Do you know the TDS of that old water? That may have been the source of all of the TDS.

The TDS should be closer to 0 ppm TDS, but again, the containers need to be totally clean to accurately read low TDS.

 

[jbird0420]

TDS of old water is around 860ppm. I'm sure it has a lot to do with the container being dirty. Last time I cleaned it was over a year ago...

No, it's a 35g trash can I use for water changes. It had about 20 gallons already made up water, before I switched out the membrane.

Do you know the TDS of that old water? That may have been the source of all of the TDS.

The TDS should be closer to 0 ppm TDS, but again, the containers need to be totally clean to accurately read low TDS.

 

[jong11]

Did you run your rodi for a bit before starting to collect

 

[jbird0420]

No, tested immediately after membrane change. Tested again after running for an hour. Water tested at 103ppm. Much lower than before..

Did you run your rodi for a bit before starting to collect

 

[Dave1NC]

I had some issues with my TDS when I installed a new 75 GPD RODI system. To improve mine I had to add a booster pump. Before using the pump my TDS out was 5-10 TDS, since using the booster pump my DI resin is lasting longer and my TDS is 0-1. My PSI was around 40 and now its around 80-90 PSI.

 

[jbird0420]

Product water reads 60ppm on the TDS. That's not good.. Also, it seems the product water is coming out in a slow stream of water instead of a fast drip.. The lines on the RODi unit are clear and not tangled. What could that be?? I don't have a booster pump on the unit. It's a 60gpd unit with a flow restrictor. I do have a 50gpd membrane. Got it from the filter guys and he said it's ok to use with that unit.

 

[Randy Holmes-Farley]

Many units have a slow stream, but if the membrane is not seated perfectly, water will leak by and quickly deplete the DI.

 

[jbird0420]

The membrane is pushed into the housing as far as it will go. Is there something else I'm missing? It did seem the DI was depleted faster then usual prior to this. Unless the membrane simply won't work with my unit. It's in the membrane housing and I can't push it down any further if that's what you mean?

Many units have a slow stream, but if the membrane is not seated perfectly, water will leak by and quickly deplete the DI.

 

[Randy Holmes-Farley]

Not pushing it down. Its how well it seals against the side or top or wherever it is sealed to prevent water from getting around it.

 

[jbird0420]

That black seal around the membrane was a tricky sucker. Ill look at it again after work. lol! Thanks!

Not pushing it down. Its how well it seals against the side or top or wherever it is sealed to prevent water from getting around it.

 

[jbird0420]

Want to thank everyone for the help and Russ @ Buckeye Supply for the over the phone help on diagnosing my problem.

It's was a combination of a bad inline TDS meter. Membrane not seated properly in the membrane housing and dirty water container.

TDS reads on ro before DI @ 9ppm and @ product water after DI 0ppm!

MIssion Accomplished! Thanks all...

You guys rock!

 

[jbird0420]

I had to use a water based lubricate to get it to seal properly.

Thanks for the help!

Not pushing it down. Its how well it seals against the side or top or wherever it is sealed to prevent water from getting around it.

 

[Randy Holmes-Farley]

Sounds good!

Happy Reefing.