RODI Unit

StPatrick89

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Using this RODI unit for the first time. I’ve got a dual TdS meter, the inlet is reading 159 and the outlet is reading 4. Does this mean I don’t have to use something like Seachem Prime, or do I still have to do this?
 

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If you have an RODI unit, it scrubs the Chlorine out already when it goes through the carbon part of the filter. The 4 TDS means you have only 4ppm solids left, which leaves little of anything. I would check whether the TDS meter is set up properly, it should be after the DI unit, so you know that you're getting near zero (usually zero) after the DI stage. Typically I'd have it After the RO unit (~4 ppm) and then after the DI (0 ppm). You'll probably always be within the ballpark of that 159 number coming out of the tap, so not a huge reason to check it. But you will want to flush the RO membrane for a minute or so to get that TDS creep out if possible so you're not burning through DI resin.
 

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TDS readings are always above "0" when the unit first generates rodi water.

You dont see "0" until about a gallon is produced.

Also. Inline TDS readers are pretty wonky and inaccurate some/most times

A true reading is from a handheld TDS meter that's calibrated


.
 
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TDS readings are always above "0" when the unit first generates rodi water.

You dont see "0" until about a gallon is produced.

Also. Inline TDS readers are pretty wonky and inaccurate some/most times

A true reading is from a handheld TDS meter that's calibrated


.
great, so I should grab a hand held one… any recommendations?

also I ran it for a good while when I replaced all the cartridges. Someone gave this to me.
 

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great, so I should grab a hand held one… any recommendations?

also I ran it for a good while when I replaced all the cartridges. Someone gave this to me.
Look at Amazon for Handheld TDS Meters...and read the reviews... and make a choice from there
 
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If you have an RODI unit, it scrubs the Chlorine out already when it goes through the carbon part of the filter. The 4 TDS means you have only 4ppm solids left, which leaves little of anything. I would check whether the TDS meter is set up properly, it should be after the DI unit, so you know that you're getting near zero (usually zero) after the DI stage. Typically I'd have it After the RO unit (~4 ppm) and then after the DI (0 ppm). You'll probably always be within the ballpark of that 159 number coming out of the tap, so not a huge reason to check it. But you will want to flush the RO membrane for a minute or so to get that TDS creep out if possible so you're not burning through DI resin.
Ok it’s set up going into the DI, not coming out of the DI. Should it be after the DI, basically the out?
 

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Traditionally they're in and out of the di. It's to see what the tds is coming out of the membrane and then checking your final tds. Other than curiosity there isn't much reason to know your feed waters tds. If it gets higher it doesn't change how you run the filter.
IMO the inline tds meters are good enough for our usage. Just make sure the probes stay perpendicular to the direction of flow and don't get turned in-line with flow.
 

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I disagree. If you don’t know your incoming tds then you won’t know if you drop below the rejection % of the membrane.
Traditionally they're in and out of the di. It's to see what the tds is coming out of the membrane and then checking your final tds. Other than curiosity there isn't much reason to know your feed waters tds. If it gets higher it doesn't change how you run the filter.
IMO the inline tds meters are good enough for our usage. Just make sure the probes stay perpendicular to the direction of flow and don't get turned in-line with flow.
 

outhouse

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You dont see "0" until about a gallon is produced.
true depending on how much TDS one has to start with.

and for OP remember takes a while to flush out new carbon blocks to get to zero. I get +1 just from new blocks for about 75 gallons
 

outhouse

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If you don’t know your incoming tds then you won’t know if you drop below the rejection % of the membrane
exactly I run incoming TDS and after membrane before DI and it never hurts to have another after DI to make sure DI is doing its job. im lucky and have low TDS incoming so 2 works for me where 3 is ideal
 

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I disagree. If you don’t know your incoming tds then you won’t know if you drop below the rejection % of the membrane.
Valid point. I can't honestly say that I regularly calculate my rejection rate. I just look for an increase in tds after the membrane to know when to replace my membrane. But now that you mention it if I had a large change upward of my waters tds from the house I could potentially replace the membrane before it needs it. So if it were only a dual tds meter where would you put them, before and after the membrane? If so how would you know when your di is depleted, unless you just go by the color change, assuming it's color changing resin. Really a triple in-line meter would be better, or a handheld for the filtered water.
 

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Really a triple in-line meter would be better
yes as I explained in detail. with dual I run incoming and after membrane and trust my DI to d its job. I know what I produce but you can always measure and move inline for a short period to after DI to ensure your making zero water
 

shadow1013

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Honestly I'd just replace the dual with a triple TDS. If you have a handheld TDS reader you could check you source every few months and see if there is any change and keep the dual after the membrane and after the DI.
Valid point. I can't honestly say that I regularly calculate my rejection rate. I just look for an increase in tds after the membrane to know when to replace my membrane. But now that you mention it if I had a large change upward of my waters tds from the house I could potentially replace the membrane before it needs it. So if it were only a dual tds meter where would you put them, before and after the membrane? If so how would you know when your di is depleted, unless you just go by the color change, assuming it's color changing resin. Really a triple in-line meter would be better, or a handheld for the filtered water.
 
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StPatrick89

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Honestly I'd just replace the dual with a triple TDS. If you have a handheld TDS reader you could check you source every few months and see if there is any change and keep the dual after the membrane and after the DI.
I was looking at it earlier and it’s cheaper just to grab a handheld for post DI than to buy a triple
 

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