hey all got a question about rain water and ionic boost,

a friend told me the best water to use is rain water, also he had me order a root enhancer called ionic boost so i wanted to get a general idea from you all here as to what you thought, i have 4 gallons of fresh rain water from a heavy rain yesterday, the ionic boost says to add 3/4 teaspoon to one gallon of water, also i am watering my plants every other day with 200 milliliters of water is that enough water once the plant sprouts how much water would you recommend i give them, i have 4 seeds that sprouted today