I had a bottle of water sitting out for a bit over 24 hours which had a ppm of ~146 ppm initially. I check now, and it has a ppm of ~167 ppm. Then I check the bottle that was siting there for 48 hours, and it has a ppm of ~163 ppm now. How can the TDS of the water go up when chlorine is supposed to evaporate?
Have you ever calibrated the meter? It could simply be off and not reading right. It should be done fairly often and right after purchasing it but it is neglected by most. Other options would be the meter probe was dirty or possibly something got in the water some how
On the manual it said it was factory calibrated, and won’t need calibration for a long time. There was no calibration guideline. Do you know how calibration is done? There is only a hold, shift and on/off button.
I wouldnt trust it saying it doesnt need to be done or that it was factory calibrated especially if it's cheap or Chinese. Back when I used them I bought some that said calibrated but read wrong. Theres calibrating solution you will need to buy in 2 different ph's. Ones a higher ph, ones a lower ph. You dip the meter in them and if it's off you'll have to consult with the company on how to change it. Maybe theres something online about it. Any quality name brand meter would have that info available somewhere. Chinese junk who knows....
I use a Hanna pH/TDS/EC meter. $265. Truly one of the great meters out there. Calibrated and confirmed too! I don't know for sure so I am just suggesting, but this is what I find. Over time the pH changes in the mix. This happens as the particles actually absorb the hydrogen ions and establish the true pH. It can take hours. Mine almost always goes up a little overnight as the PPM's adjust. All three affect each other. I watch pH and PPM's bounce as the meter figures it out. PPM's is EC x .5 in this case. I work off the .5 scale. You can do .7 too. So it's all just math. The other thing, I have found, if you are using organic nutrients, is I have to stir them to stabilize the pH. The nutrients settle to the bottom. That should also mean a recalculation of PPM's. That is what I find.