pH of 4.9 is too low if you are using cow's milk. The curds must have a pH of 5.1-5.3 in order to stretch. I only make mozzarella using water buffalo milk and it requires a pH of 5.0 to stretch. I read that using calcium chloride in a mozzarella is counterintuitive because the curds release calcium as it acidifies. To be honest your mozzarella still looks nice.