boil "open milk tea". Sorry I don't know how to type chinese. Try to give baby 1 time a week. one bag can make about 240ml (5 bottles).
My son is drinking s26, I boil 2 times a week.
my bb is also 13 months and got the same problem. I give her prune juice (Del Mont) and the "king banana" (the small one), they really work so it's worth to try!