EC/PPM of nutrient solution dropping

I am kind of stumped by this and cant figure it out by googling. I'm growing in coco/perlite and I'm feeding 1.5 EC using Jacks 321 and tap water. I'm trying to mix a couple of gallons and then use as I need but when I check my solution, that is bottle and covered the EC is drifting down. I make sure everything is well stirred, shaken, etc. I can understand a PH drift but not EC. For example last night I mixed 1 gallon and my EC was 1.6 and now its 1.3. What could be causing this?

"The EC values ranged from 17.33-19.47 mS/m. The highest EC at 0 day storage times, and the lowest EC at 45 days storage times. There was a change of EC values of slurry. EC values during storage times decreased (T able 1). The change of EC values showed that there were changes of ion composition in the slurry, because . . . ."

Just mix it as you need it.

That’s a pain in the ass though when you are fertigating 2 times a day in coco

pizzax1 said:

That’s a pain in the ass though when you are fertigating 2 times a day in coco

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Ah.... the prices we pay to grow our favorite plant.

well, I guess if its a normal thing then silly me for not thinking about it. I'll do the same I do to counter PH drift, mix the EC higher, dilute as needed and expect the drift. Thanks though guys.