RODI water TDS reading 3ppm

[MartyF]

I bought a 5 stage RO/DI system from BRS about 2 months ago. I finally got a TDS meter and is reading the water produced at 3ppm. Is this an acceptable range for a reef tank or should it be 0?

 

[mich2599]

Zero is always preferred. What is your TDS before DI?

 

[redfishbluefish]

Yes, you want zero after DI.

What is your source water TDS, and post RO?

Also, where does your water come from...well or city water?

At first glance, looks like you need to replace DI resin.

 

[MartyF]

Yes, you want zero after DI.

What is your source water TDS, and post RO?

Also, where does your water come from...well or city water?

At first glance, looks like you need to replace DI resin.

Water source is city water at 167ppm

 

[redfishbluefish]

OK, so a quality membrane has a 98 percent rejection rate. That tells me that TDS you are seeing is membrane (RO) only....most likely your DI is spent.

Let's get a little more information. Might be able to considerably extend the life of the DI resin.

How frequently do you make water, and how much do you make at any one time?

 

[MartyF]

I average about 20 gal per week, usually make 5 gal at a time

 

[redfishbluefish]

So you start and stop your unit say, four time a week.

This will help save your DI resin.....a tee valve to run the first five minutes to waste before sending it to your DI resin. Let me explain...Every time you start your unit you get breakthrough TDS. For me, it shoots up to 50 or 60 or so, and then comes down. I can see this because I have an in-line TDS meter between my membrane and DI resin. Now I also have a tee valve there too! Here's the kind of tee valve I'm talking about:

BRS sells these HERE. Again, this is installed between the membrane and DI resin. When you first turn on your unit, turn the valve so that water goes to waste. For me it takes about five minutes before the breakthrough TDS comes down. Then turn the valve to start to make "good" water by sending it through the DI resin.

This will greatly extend the life of your DI resin. Mine lasts me about a year. Hope this helps.

 

[SDK]

I have the same unit and I effortlessly get my 260 tds water down to 0, so I’m going to ask a dumb question. Are you sure that the switch on your tds meter is over to the right and reading the post DI number? If it’s to the left it’s reading the water heading in.

Asking because around 3 tds is what I’d expect to see from your water after the RO membrane but before the DI stage....

Edit- just realized you added the tds meter on to an already used RODI. I would agree that you probably need new DI resin...

 

[MartyF]

So you start and stop your unit say, four time a week.

This will help save your DI resin.....a tee valve to run the first five minutes to waste before sending it to your DI resin. Let me explain...Every time you start your unit you get breakthrough TDS. For me, it shoots up to 50 or 60 or so, and then comes down. I can see this because I have an in-line TDS meter between my membrane and DI resin. Now I also have a tee valve there too! Here's the kind of tee valve I'm talking about:

BRS sells these HERE. Again, this is installed between the membrane and DI resin. When you first turn on your unit, turn the valve so that water goes to waste. For me it takes about five minutes before the breakthrough TDS comes down. Then turn the valve to start to make "good" water by sending it through the DI resin.

This will greatly extend the life of your DI resin. Mine lasts me about a year. Hope this helps.

Wow, thanks for the great info! Really appreciate it.

 

[sandswhitson]

I also dump the first but of my water to the drain before the DI as redfishbluefish does. I have mine setup through my Apex with some solenoids that dump it for 5 minutes then solenoids switch and send the water to my DI and water container.

 

[Opus]

Really need your tds reading after the RO membrane. Something just doesn't seem right. As stated earlier, with 167 tap water I would expect somewhere around a 3 tds after the RO membrane. With 3 going into the DI you should expect to make around 1400 gallons of 0 tds water. Even not doing the by passing, it isn't going to deplete it in 2 months. I do about like you with 450 tds tap water and my DI will last 6 months to a year and I don't bypass the DI initially.

 

[Flippers4pups]

Aside from DI possibility of depletion, TDS creep could factor in initial start up.

 

[MartyF]

Aside from DI possibility of depletion, TDS creep could factor in initial start up.

Thank you to all! So helpful, love this forum and the people on it. I ordered the valve and DI resin and will let you know the results.

 

[LBCobra]

I would replace the DI.

 

[MartyF]

So you start and stop your unit say, four time a week.

This will help save your DI resin.....a tee valve to run the first five minutes to waste before sending it to your DI resin. Let me explain...Every time you start your unit you get breakthrough TDS. For me, it shoots up to 50 or 60 or so, and then comes down. I can see this because I have an in-line TDS meter between my membrane and DI resin. Now I also have a tee valve there too! Here's the kind of tee valve I'm talking about:

BRS sells these HERE. Again, this is installed between the membrane and DI resin. When you first turn on your unit, turn the valve so that water goes to waste. For me it takes about five minutes before the breakthrough TDS comes down. Then turn the valve to start to make "good" water by sending it through the DI resin.

This will greatly extend the life of your DI resin. Mine lasts me about a year. Hope this helps.

I flushed the water for 5 mins before heading to DI resin and replaced DI resin and I am now getting 0 TDS readings on my water. Thanks again for all your help!

 

[Flippers4pups]

Your welcome!

 

[Tuan’s Reef]

My barracuda gets 5-6 tds before hitting the DI. This normal? My city water is at 150-160 tds.

I do get 0 tds after DI though

 

[Liron Mishal]

My barracuda gets 5-6 tds before hitting the DI. This normal? My city water is at 150-160 tds.

I do get 0 tds after DI though

calculation as follows:
((tap water TDS - output TDS) / tap water TDS ) * 100= rejection rate in percentage.

tap tds of 160 and output of 6 gives a rejection rate of 96.25%. not bad