Neutrogena shampoo should only be used 3 times a year if needed to remove residue from dreads, rinsing it out very very well.
If you like to use shampoo, order from dreadlockshampoo.com for residue free, natural dread products. Your baking soda ratio is 1/2 cup BS to 5 cups water. leave on for 10-20 minutes to exfoliate the scalp & rinse out well before doing the ACV rinse. Your head will love it if you finish off with a cold rinse too. Peace