RO/DI water

[reefmaster70]

Ok, dumb question, I have my 4 stage RO/DI unit, newer cartridges, the digital TDS meter that is built in shows me like 120 TDS going in and the meter reads 0 tds going out. GREAT! I also have a small handheld TDS meter, and i make up 5 gallon buckets of water at a time, put a lid on them and store them in my hall closet for maybe a week to 10 days at a time. Now, here is where it gets weird, when the bucket sits for several days and I check the water with my handheld TDS meter it will read around 26 TDS in the water that had previously tested 0 when it was fresh out of the unit. Why is this? Can anyone explain? Thanks

 

[Fish Fan]

RODI water is nearly pure water, and water doesn't "want" to be pure. It will react with nearly anything and everything, including things in the air or even residual salt in your mixing bucket. In nature, water is never pure, except for in the clouds when it's first precipitated. As soon as rain starts to fall, it reacts with things in the atmosphere and by the time it hits the ground it's no longer pure water. Think acid rain here. I hope this helps you understand what's going on with your RODI water :)