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Discussion Starter · #1 ·
I have what is essentially 4 TDS meters (2 dual channels) that I use on my RO/DI unit. Accordingly, I measure the source TDS, the TDS levels after the sediment and carbon blocks, the TDS after the RO and the TDS after the DI unit. I only started measuring the source just because I wanted to get an idea of the ratios of blending of RO/DI water and post sediment and carbon block water. This approach enables me to provide the Macro elements that I would otherwise have to dose as shown below. It works great with my auto water changer. The only surprise is that after monitoring the source TDS for some time now, I have seen a huge variance in the water quality measured by TDS. I have seen it as low as 117 and currently as high as 320. Fortunately, my RO TDS measurement is almost always at 0 or 1 and my DI is always 0. With this current rise in my TDS source levels I have notice that the RO TDS is 1. This really isn’t bad but I had gotten spoiled with it producing a TDS of 0. Just wanted to see if anyone else sees that type of variance in their water source. This link shows what is considered to be acceptable levels for drinking water.

TDS total dissolved solids water quality testing - TDS Meters & Testers



JT
 

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TDS can be made up of many different elements as i'm sure you know. i work in a lab that tests municipal water and Yes, it is very common for water to change in the amount of TDS depending on the time of year and what is happening with the system. I assume your units measure TDS by conductivity, conductivity being the ability of water to carry a current. This method simply uses a calculation (0.67x#microsiemens) to determine TDS.

I don't know much about RO, but if your unit is not producing water with a no TDS wouldn't you want to either slow the water down so that it can be deionized better or replace the membrane and/or solution?

Our tap water here has a conductivity of <20, so very low TDS. Reagent grade water in our lab has a conductivity of <1.0, so a TDS of <1.0 is very very negligable. I mean, we have equipment that tests for calcium, magnesium, iron, and all the other anions and cations and we use water of 0.7 TDS without affecting our test results.

Kara
 

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Oh, and a final thought, do you calibrate your meters? Go buy some distilled or deionized water or even some bottled water that lists the TDS as a reference point.

Kara
 

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Discussion Starter · #4 ·
I don't know much about RO, but if your unit is not producing water with a no TDS wouldn't you want to either slow the water down so that it can be deionized better or replace the membrane and/or solution?
Kara, thank you for your response, especially since you work in a lab that test municipal water. It does explain the disparity. The RO/DI unit I use as a restrictor that slows the flow to 50GPD. The TDS reading of 1 was only after RO and only since the source went up to over 300. Normally I get TDS readings after RO of 0 and always get TDS of 0 after the DI cartridge.



JT
 

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No problem, not much help. Your knowledge on what's going on is probably more extensive than mine. To us the values don't matter too much, we have a range as long as our water is within it we are fine, if not then we need to adjust something.

Sorry if I'm being nosy, but what is the purpose of having such 'clean' water? I am guessing it is simply because your source water is just so 'dirty' or hard?

kara
 

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Where does the Reston, VA water come from? Surface (river or reservoir) is common in the southeast - there is a TON of variability there. Also, some suppliers will change sources or blend sources at varying levels during the year.

As Kara said, you do seem to be very concerned about something that wouldn't bother most people/fish (total TDS) - how much of your TDS is due to hardness ions (what is your GH)? Is there something else you need to remove?
 
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