Fluxuating TDS Results

So I was testing my RO/DI water and my TDS readings were all over the place. It went from 8 to 0 to 76 to 19 in about 10 seconds. Any ideas why this is happening?

 

What are you testing with, what are you testing in and how long did you let the system run to stabilize before testing? Could have been TDS creep if it was in the first few minutes of starting the system.
Some TDS meters are not auto temperature compensated so can be all over the place unless the water and air temperature are exactly the same and stay relative steady without fluctuation up and down.

When you take a TDS reading you insert the meter in the water and let the reading stabilize, it will not be steady or accurate until that point.

 

I'm using an HM TDS meter and I'm testing in a bucket of fresh water that I filled up about a week ago. I'll try and test it for a longer amount of time.

 

Which meter? The TDS-EZ is not temperature compensated, neither are the dual inlines. The TDS-3, TDS-4TM, AP series and COM-100 are so should be accurate quickly since they have a temperature probe in the water.

When you test out of a bucket, especially one that has been sitting you are not seeing the same thing the RO or RO/DI system produced if that is your goal. You need to test directly from the RO membrane and the DI resin to troubleshoot a system. Make sure you triple rinse your meter, cap and a clean glass if you use one in RO/DI or distllled between each test and after you are done so the meter probes stay clean for next time and your readings are accurate without scale or buildup.

 

When you test out of a bucket, especially one that has been sitting you are not seeing the same thing the RO or*RO/DI*system produced if that is your goal.

What do you mean by this? I've noticed that the TDS of my RO water in storage rises over time. What causes that?

 

RO and especially RO/DI water are very agressive, they have been stripped of all their ions and are trying everything to get back to their natural "dirty" state. RO/DI will pull contaminants out of the air, attract dust, pull solvents out of some plastics, eat any metal short or titanium and more. Utrapure is not its natural state and it wants the ions, lcium, magnesium, manganese, iron, copper, nitrates, phosphates and all the other stuff you removed from it back.

This is why it is important to seal or tightly cover RO/DI water so it stays pure. Almost everything you removed registers as TDS so it will gain TDS once exposed to atmosphere.

I store my ATO water in a covered Rubbermaid can and water change water in capped 5G drinking water type jugs. It stays 0 TDS for a long long timeif kept that way and not aerated or having dirty tools, buckets and such dropped in it or stickimg your hands in it.

 

That's probably the problem, then. I'll try testing straight from the unit. I'm using a DM1 Dual Inline meter. I just never installed it in the unit. I should probably do that now.

 

Water is a solvent as AZ has thoroughly explained.K+8)
I always treat my wc container like a temple.Plastics can be a sponge.

 

You cannot use an inline TDS meter as a portable and stick the probe in the water. They must be installed inline using the tee and the probe must be rotated in the correct direction with flow going through the tee. Sticking one in a glass or bucket does not work with any degree of accuracy and is your probem. I have two DM-1's and never even use them since they lack the accuracy and portability of a good handheld which is temperature compensated and very versatile. The readings never agree with the handhelds.

 

So if mine will be inaccurate even after I install it, what TDS meter should I get?