TDS rising over time?

[MarkW19]

I tested my RO (non-DI unit) water when it'd finished in my waterchange container (15gal), and I got a good reading of 4ppm from my TDS meter, which is exactly the same as I got the week before with my previous batch of RO water. So all was good.

However, after leaving the water in the container with a loose lid on it in my bathroom, for 4 days, I've just tested my water again and it's now gone up to 23ppm.

Anyone any ideas?? I've not touched the water since, and there's nothing else in the container (which is in fact a plastic aquarium).

 

[dustybrannum]

When I ordered my RO/DI system from AquaFX they suggested I get the water tank with it because many consumer plastic containers will leech minerals into the water because it is so pure. HTH

 

[MarkW19]

That may be it, but it is a dedicated aquarium, so you'd think it'd be non-toxic etc. Also, an extra 20ppm is a lot to "leech"...

The funny thing is, when I first got my TDS meter, I tested a small sample of RO water into a small plastic container and it came back as 23ppm...

Then, the next 2 proper runs I did, I got 4ppm...

Don't know what's going on really.

Perhaps it is the container(s).

4ppm was better, but I'm still fairly happy with 23 (down from 140 from my tap!).

 

[dustybrannum]

only 140? mine goes from 197 to 300ppm on the tap

 

[Leaf]

On the off chance.. Does your TDS meter need to be recalibrated?

Are you testing the RO water from a smaller container such as a plastic or glass cup?

Make sure this cup (or other container) is very clean since any remaining residue could influence your test results.

As far as other reasons or the cause for the changes.. I don't know. :?

 

[MarkW19]

Apparently my TDS meter doesn't need to be calibrated - there's also no way of doing so, so I guess not.

I'm testing my RO water straight in my tank (the plastic tank I use for waterchanges).

 

[Atari]

Try it again later.. I'm still convinced these meters have an accuracy of +/- 20ppm.

 

[MarkW19]

Well, I've just put my salt in now - I'll test a few times at my next waterchange

 

[reefrunner69]

loose lid...dust....

 

[MarkW19]

Hehe, maybe so!