True. When PH is too far off, certain minerals may be locked out.
I always try to top off the reservoir through the week. This allows me to add ph’d water which pretty much stabilizes the PH for a day or 2. I also find that my ph does not waiver as much, as long as I do not go past 2 days before topping off with ph’d water.
Another important thing to know here is: You can only top off with ph’d water until you have used as much as the reservoir holds. i.e. If you use a 5 gallon bubbler; Then you cannot add more than 4 gallons of ph’d top off water before adding a fresh batch of ph’d nutrient solution.