fluxuating TDS readings on my RO/DI output water *%$@#$%$@!%

[cdeakle]

I have a Kent Marine Maxxima Hi-S 35GPD RO/DI unit with optional flush kit and x2 Hanna TDS1 meters for double verification.

I find that my RO water fluxuates between 2-12 or so TDS even after all new filters and flushing. It take a few batches before I can get the tds down to 0-1 TDS and even then it could rise again within 5-15 gallons.

I cannot find a pattern of anykind other than I have to run the filter for some time and after a few flushes and anywhere up to 15-20 gallons I finally get 0-1 TDS.

Any ideas? The only thing I can think of is I use 5 gallon water jugs to fill ro water with then I add salt to the same jugs. After water changes I rinse these jugs out, drain, and then refill with new ro water. Could there be some salt residue of some kind left over thats throwing my readings off? I really don't think so but thats the only possible scenario I can think of.

HELP please before I drop kick this 200 dollar some-um-of-iatch out the window :evil:

 

[taikonaut]

CO2 in the air will affect your TDS reading if you let the sample out for an extent amount of time. Verify this by degasing the water sample and leaving it out for a few minute. RO/DI water suck up CO2 in the air like a sponge. Even a small amount of leftover salt in the sampling bottle will increase the TDS up a bit. Verify this by adding a grain of salt into the water sample.

Test the accuracy of your meter by testing water of know TDS reading. In another words, make sure your meter is calibrated. Sounds like it is not off much, if at all.

If you ever want to kick that perfectly good filter out the window, I have a mailing address for you to sent to with postage prepaid.

 

[cdeakle]

If you ever want to kick that perfectly good filter out the window, I have a mailing address for you to sent to with postage prepaid.

:lol:

I rinse and drain the water juggs thouroughly and I have 2 tds meters calibrated perfectly and both give the same readings. So I have ruled those options out.

CO2 in the air will affect your TDS reading if you let the sample out for an extent amount of time. Verify this by degasing the water sample and leaving it out for a few minute. RO/DI water suck up CO2 in the air like a sponge.

Never would of thunk this one. How would I "degas" the water?

 

[WannaBeReefer]

I think a simple air stone will do the trick

 

[Tremelle]

I use the Kent Marine Maxxima Hi-S 65GPD RO/DI and see the same thing. I use a 32 gallon Brute trash can for my water. I also mix my saltwater in the same can. I have notice a reading around 22 on my RO/DI. It is due to the salt that has been mixed in the can. Plus the can has a lid but it is not air tight, so CO2 is also being absorbed into the water.

 

[taikonaut]

In the lab, we boil the water for a few minutes to get the dissolved gas out. For household, use a microwave to heat the water to be sampled. I guess that is too much trouble for most people, so you just have to live your slightly impure water contaminated with deadly CO2 gas

In all seriousness, I do think you did not use the right container to sample the water. Even a slight residue can give you noticeable reading on the meter, as mentioned above. When I use my meter to do reading, I let the water run into the sampling well (sensor) for a few second even before I turn the meter on.

I don't want you to be over concerned about getting the TDS under 1ppm, but for a properly working DI, you should not get any reading from the TDS meter because it is not designed to do measurement in such ultrapure water.