Is more PoolRx better? Can I overdose?

No, more is not better. There is a wide range for error on sizing, but Yes, you can overdose. If you add too much mineral to the water, the granular mineral won’t have room to dissolve into solution. It can stay in granular form (a blue-ish color) and it will settle to the bottom and or float around and stick to the scale turning it a blueish color. See FAQ 24: I made a mistake. How do I fix it?