Do not worry too much about the yellow on the leaves as it only the oldest leaves that show yellow margins. This could be old age as the oldest leaves must drop as new foliage appears. It could also be a sign that some plant food like Osmocote would be appreciated especially if the plant has not been fed for a year or more.  Some plants are also sensitive to fluoride or other chemicals in tap water. You could pamper your plants by using distilled water. Otherwise, your plant looks pretty happy. Keep growing, Marianne Binetti