Hi, 2Sheds.
I mix my nutrient solutions in 5 or 6.5 gallon buckets following GWE's GH Trio + CalMag nutrient solution mixing guidelines for coco coir. I usually mix two buckets of nutes and two buckets of plain, pH'd, tap water. The 20 to 25 gallons of solutions lasts me about a week for 10-12 plants in 7 gallon fabric pots (in outdoor greenhouse grow). I do get a little pH drift towards the alkaline side from a pH 6.0 starting point. I'll adjust down if it gets too basic. Most of the time I do not even check it and the plants grow perfectly fine. Simply check the pH and adjust, if needed. I do not believe the chemical makeup of your nutes will signicantly change over a week.