RO/DI Unit

[kelley_mc]

I have a question about my RO/DI unit. I recently bought the Typhoon 5 stage. It works great.

My tap water has a TDS of 34 and the RO/DI has a TDS of 0. I have a TDS alert after the RO membrane that constantly monitors the TDS of the water coming out of it and notifies me when the TDS out of the membrane is higher than 30. No problems and everything seems to be working fine.

However, I have a color changing resign in my DI canister that changes from black to a rust color as it is being exhausted. So far I have made about 20-25 gals of RO/DI water and the color change is at least an inch and a half to two inches up from the bottom. At the current rate, I estimate that I will have to change the DI resin at around 130 gals. Does this seems correct? I have such a low TDS in my tap water that I expected the DI resin to last a long time.

Thanks!
Kelley

 

[Misled]

Morning Kelley, Don't use the color change as the time to change the di, it can be used as a ballpark guess but the water tends to channel through it. Use the TDS meter to judge the condition of the di. When it stays on 1 or 2 continually then it's time to change!

 

[AZDesertRat]

Color changing resin is a very poor indicator of condition. Rely on your TDS meter and forget the colors.

 

[kelley_mc]

Thanks for the responses. I may not have asked the question correctly...

I have the TDS meter that will notify me when I am not longer getting 0 TDS and that I should change the DI. I thought that the color changing resin was actually a poor indicator because usually the TDS starts to creep up before the indicators colors indicate that a change is required. If that is the case, I may not even get 130 gals out of my DI with water that has low TDS to start with.

Does that seem correct? Or am I missing the point and the DI cartridge color change may be completed rust colored indicating that it is exhausted but it will still work just fine?

 

[AZDesertRat]

Tape a piece of paper around the canister and ignore the color. It tells you nothing, in fact they add dyes to color changing resin that can actually be recorded as TDS so you will never get semiconductor grade water of 18.2 megaohms with color changing resin. Next time you replace it get non color changing, it will perform better.
What is your RO only TDS without DI? Thats the number that will tell you how long the DI resin will last.

 

[kelley_mc]

<a href=showthread.php?s=&postid=9220374#post9220374 target=_blank>Originally posted</a> by AZDesertRat
Tape a piece of paper around the canister and ignore the color. It tells you nothing, in fact they add dyes to color changing resin that can actually be recorded as TDS so you will never get semiconductor grade water of 18.2 megaohms with color changing resin. Next time you replace it get non color changing, it will perform better.
What is your RO only TDS without DI? Thats the number that will tell you how long the DI resin will last.

I knew you were going to ask me that...

The tap water is 34, the RO/DI is 0 and the RO water is somewhere less than 30. Anything over 30, and the TDS alert notifies me.

I don't have an actual reading on the RO water though. My guess is that their really isn't much of a need to have the TDS meter on the tap water anymore. The instructions said that I should put it there but I am not sure what good it does. Should I just move it to the output of the RO, inline with the TDS alert?

 

[kelley_mc]

Oh, also, what TDS should be coming out of the RO unit?

 

[AZDesertRat]

I was thinking that unit also came with a handheld TDS meter? I monitor my tap water, pre RO but after the prefilter and carbon block, after my RO only and after my RO/DI to trend any changes. Its important to know ehat your RO is doing as it is what controls how well your DI is doing and how long it lasts.
TDS out of the RO should be less than 1 if your tap is only 34. You will not be able to measure that low with the inline meter but a HM Digital COM-100 handheld will measure that low with accuracy.

 

[kelley_mc]

I do have a handheld meter, I have never used it though. It was a cheapo one, I got it for less than $30.

Having the dual in-line meter, what is the best location for the other probe? Obviously, one needs to go on the RO/DI output. My feeling is that the tap water TDS is the least relevant. With the output of the RO the most? Obviously it would be nice to also see the TDS of the water going into the RO.

What do you think? Move the "In" probe of the meter to the output of the RO or to the input of the RO?

I can test my tap water easily enough with my handheld to watch for any changes.

 

[AZDesertRat]

Post RO and finished water would be most useful. You can always test the tap with the handheld easy enough.

 

[kelley_mc]

Great, as always, thanks for all the help!

Kelley