Where to Install Inline TDS?

[cham]

Obviously I would want one of the meters on the exit of DI that will show final TDS reading of water (hopefully always zero) but what I was wondering is where to put the other.

I would think in the line exiting the RO heading towards the DI. That will let me know when my RO needs replacing....right?

I've seen some put it on the incoming line to tell you what your tap water TDS is but whats the point of that? I have a hand held if I want to know that one.

 

[J Castellano]

No, you know when your carbons need replacing by testing for chlorine (get a test from any local pool store) the ot her meter is ment for your incoming water just as a reference to see what your intial tds is. They are made like this because the inlines are meant for other uses that only require an 80 % efficiency at allows people to regulaate this. Whereas us reefers need 100% efficiency.

Justin Castellano

 

[cham]

No, I was saying AFTER the RO but BEFORE the DI so I could see when my RO membrane was starting to wear out i.e. it reads 1 or 2 for a year or so and then starts creeping up.

Anyone know if this is a good thing to do?

 

[puddldude]

i have a dual so one is right before it enters the unit and one sensor right after it leaves the unit. I think I paid 20 bucks a few years back for it

 

[AZDesertRat]

If you have a dual meter you want the first probe after the RO membrane and the second probe after the DI filter.
I have two inline meters so I have the probes like this
1. After the prefilter and carbon or pre RO
2. After the RO
3. After the first or MaxCap DI
4. After the second or SilicaBuater DI or final effluent/product water.

Even though I have them I am not a big fan of inlines for a couple of reasons. One is they are not truly temperature compensated and actually read air temperature and not water temperature. If your air and water are not the same temp the TDS readings can be significantly off.
Another is they can not be calibrated and I don't trust anything I can't clean and calibrate.

A much better choice is a handheld HM Digital COM-100 conductivity/TDS meter. It is 10x more accurate and 10x more sensitive than the inlines, even their own, and it can be calibrated in three different modes for extreme low end accuracy.
Also since it is portable you can test tap water, bottled water. store water or anything else with it.

 

[cham]

<a href=showthread.php?s=&postid=9601644#post9601644 target=_blank>Originally posted</a> by AZDesertRat
If you have a dual meter you want the first probe after the RO membrane and the second probe after the DI filter.
I have two inline meters so I have the probes like this
1. After the prefilter and carbon or pre RO
2. After the RO
3. After the first or MaxCap DI
4. After the second or SilicaBuater DI or final effluent/product water.

Even though I have them I am not a big fan of inlines for a couple of reasons. One is they are not truly temperature compensated and actually read air temperature and not water temperature. If your air and water are not the same temp the TDS readings can be significantly off.
Another is they can not be calibrated and I don't trust anything I can't clean and calibrate.

A much better choice is a handheld HM Digital COM-100 conductivity/TDS meter. It is 10x more accurate and 10x more sensitive than the inlines, even their own, and it can be calibrated in three different modes for extreme low end accuracy.
Also since it is portable you can test tap water, bottled water. store water or anything else with it.

Thats what I was thinking, have one right after the RO to monitor my membrane and the other after the DI monitoring my final product. I have a cheapo hand held to monitor my final product as well but since all these TDS are cheapos I am religious about changing out my prefilter and carbon EVERY 6 months and my DI the very first time I see anything other than dead zero. Even if it flickers to 1 for a second I change out the DI (usually change the carbon and prefilter with DI even if they don't need it)

Sound like a decent plan to have good RO/DI water?

What is a good range for the first probe (right after membrane) to stay in? What I want to know is what reading would tell me its time for a new membrane.

 

[AZDesertRat]

If you have a 75 GPD Dow Filmtec or even an Applied Membranes or GE Water membrane you should be seeing a 96 to 98% reduction in TDS between the tap water and RO only water. So just for giggles if you have a tap water TDS of 250 which is the national average, you should be seeing no more than 10 TDS after the RO only. If ts much more than that DI life can be greatly reduced.
A very accurate rule of thumb is 16 oz of DI resin will treat 2000 total TDS before it is depleted, so if you have a normal 24 oz vertical refillable DI canister and cartridge you should be able to treat about 300 gallons per refill if you have an RO only TDS of 10.
Now another very important point, for every 2% you increase the RO membranes efficiency you DOUBLE the life of the DI resin so if your membrane is 98% efficient rather than 96% efficient you will now get 600 gallons of DI out of that very same cartridge!
See how RO membrane quality really matters?
If you have a 90% efficient membrane such as the Dow Filmtec 100 GPD or some of the no names and knock offs it very quickly pays to upgrade to a better membrane ASAP. I actually prefer the Spectrapure hand tested and guaranteed SpectraSelect membranes myself. Mine is averaging 99.25% so far and its 8 months old now. I just made some DI water and my tap water TDS was 852, RO only TDS was 6.2 and DI was less than 0 with a COM-100 meter. That's an RO rejection rate or efficiency of 99.27 %! For me at a TDS that exceeds 800 it doesn't make sense to have anything less than the best.

 

[cham]

Not sure who makes my membrane. I bought my unit from an RC sponsor purely H20. I think its either 75 or 100 gpd.

My tap water TDS is 130.

 

[AZDesertRat]

It would be a Dow Filmtec then. Hpefully you bought the 75 GPD and not the 100 GPD. I think they usually try to talk people out of the 100 GPD since its much less efficient.
An easy way to tell is to test your RO only TDS. If you know your tap TDS is 130 then the RO only should be in the 2 to 5 range if its a 75 GPD and in the 13 to 15 range if its a 100 GPD.

 

[cham]

Well I got it in today. I installed the "in" line at the exit of the RO membrane and it started at 3 tds when I first fired it up but quickly went down to 1. Its staying stable at 1 right now so I would assume I have the 75 gpd unit.

I did just replace my prefilter and carbon, plus my tap TDS is already pretty low at 130.

 

[cham]

Hmmmmm, after running it for a couple hours its showing a zero TDS right after the membrane but before the DI.

I am sure it cannot be zero TDS after the membrane. Even with the low TDS my tap water has. I imagine the real number is just pretty low at 2 to 5 TDS. The real reason I bought this was to monitor my membrane so I know when to replace it. Instead of burning through DI resin before you figure out why its happening.


Would it be fair to say to replace when I start getting readings in the 5 to 10 tds range after the membrane or should I look for lower readings than that? The membrane is right at a year old now.

Thanks!
Charles

 

[AZDesertRat]

Use inline meters as a guide only, they are not temperature compensated and can be inaccurate especially at low ranges. I only trust a handheld meter even though I have two inlines in my system.