TDS going up in container

[bromion]

My RO/DI fills a 55g drum that's covered. I have had it for over a year and cleaned it out a few times. It appears that the TDS of the water sitting in the container keeps going up. When I first filled it, it was nearly zero, now it's 20ppm after a two months. The water is not just sitting there, of course, I use it all the time and the barrel gets refilled automatically. The RO/DI filter reads 2-3ppm on the output, which goes directly to the barrel, which now reads 20.

Is this normal? Any ideas?

[Boomer]

When is the last time you cleand that EC probe ?

[bromion]

How do you clean the TDS probe? I don't think it's the probe, since it matches the one I have under the sink with the RO/DI system.

[Randy Holmes-Farley]

I would not worry about that small TDS rise. A little salty dust from the air can do it, for example, ands can just a little salt contamination. :)