Hi. Thanks for your query. Noted the history about your 4 month old baby and understood your concerns. As per the history you have provided the change in stool of your baby to gray, fishy smelling is most probably due to the water that was not completely made sterile; it take more than 20 minutes of boiling for the water to be sterile. Henceforth remember this so that the care is taken to completely make the bottles, feeders sterile. Another possibility can be the changed formula as there may be a problem with the powder itself. Obviously, you should consult the pediatrician to discuss further, have clinical evaluation of the baby and stool test to know the cause and get treated properly as needed. As for the reflux, the babies do not have acidity issue. This may be due to lax lower esophageal sphincter or tight pylorus or even pyloric stenosis which needs further tests of water soluble contrast medium study of esophagus, stomach and duodenum. If anything positive is found out, get treated accordingly.