RO/DI Top Off - TDS Reading

I use RO/DI water for my top-off water. I have a 5 gal. plastic container that I use as a reservoir for the water. I keep a Maxi-Jet 400, running continuously in the container also. While I was adding newly made RO/DI water to the container, I decided to test the older water with my hand held TDS meter. To my surprise, I got a reading of 0.18 ppm. When I placed that water in the container, (newly made about 3 days ago) my TDS reading was 0.00 ppm. Is it normal for the TDS readings to increase while in the container? If not, what could be the explanation for the higher TDS reading? I should also mention that I keep a cover-lid over the container at all times.

 

I’m no expert but I have read of people testing the presence of Nitrates in their RO/DI water after it sat for a period of time. It is possible you are picking up material through the Maxijet? Has it ever had any other job than in your Top Off bucket?

 

No on the use of the Maxi-Jet. I just used it for mixing synthetic salt for a water change. And, my nitrates are consistently tested at 0 (using API test kit). Could the plastic container be leaching something?

 

There it is...that will pick up some TDS right there.

 

+1 Nor Cal Guy

 

Thanks everyone, that (Maxi-Jet) must be the culprit.

 

Its 18 TDS no decimals. Thats pretty high but is more than likely due to CO2 in the air and possibly residue in the container.
Hobbyist grade TDS meters all read in whole nunber with few exceptions like the $50 HM Digital COM-100 which reads to one decimal point as in xxx.x, it is the only one I am aware of and its only tenths not hundreths.
I wouldn't recirculate the water unitil a few hours before I use it, no resaon to do it.

 

I have to disagree, that reading is more likely form salt residue in the pump, not co2. I sold filters for years. Just my opinion. Carbon filters water, can be a tds, but not likely if you ask this guy.

Hand held pens are close at best; although a good measure for the purpose in which reef hobbyist use them.

 

Thanks AZDesertRat and No Cal Guy. Your right, of course, AZDesertRat, about the hand held meter, no decimals. I use the "HM digital TDS-3". I think the high TDS reading could have been due to a Co2 issue, contaminated container, as well as the Maxi-Jet. I did use the Maxi-Jet to mix my synthetic salt mix. So, its probably a combination of all 3 suggestions and all 3 being correct. Again, I'm just glad both you guys were there to help.Thanks again everyone.

 

RO/DI is extremely agressive, it will attract anything to try and get back to its natural "dirty" state. It will pull things out of the air as well as from plastics and tools/pumps, your hands etc.
The TDS 3 is a good meter, I used the similar TDS-4 for years before getting my COM-100 and never had a problem with it. Make sure you rinse the meter and measuring container such as a clear drinking water glass in DI water after each use and put it away clean and capped and it will last forever.