We would not recommend mixing fertilizers such as the Grow More 17-8-22 Bromeliad Plant Food or any other similar concentrates ahead of time. Allowing the product to sit in water will break down the nutrients and make the product less effective.
Per the Grow More 17-8-22 Bromeliad Plant Food instructions, You will use 1/4 teaspoon per gallon at each watering.
Fertilize with Caution:
The nutrient breakdown of Grow More 17-8-22 Bromeliad Plant Food is as follows:
Nitrogen - 17%
Phosphorus - 8%
Potassium - 22%