2 tsp a day is a standard dose for a bubs around 20 lbs
Are you going to switch back to standard formula? Regardless of the low level of probiotics in the HAF, I would start him on a separate probiotic... the concentration and quality of the probiotics in the formula won't do much to help him out.. I use BioGaia and they are amazing!!! You can get them at the pharmacy behind the counter (they are refrigerated so you have to ask for them). They are about $40 but last a couple of months
The dose for a baby is the same as an adult - 5 drops
DD started pooping so much better with 2 days of the BioGaia... I was able to stop the Miralax after a week of using both together... she was on Miralax for almost 2 months and was the same as your LO... miss half a dose and would get backed up again...
Funny enough, my cat is taking them right now too to help her out while on antibiotics
The whole family, including the four legged kids can use them