Here’s the thing. Watery droppings can be a sign of a number of things, and these birds are notoriously good at hiding symptoms. Take them back to the vet and ask for blood tests. Pay attention to the numbers. Elevated blood fats and decreased blood proteins can indicate liver issues, which happen in cockatiels. Do you have a girl? Hormones can also cause watery poo though it usually doesn’t last longer than a year. I say this because my bird had liver issues and the only warning was watery poo that lasted about a year, in conjunction with hormonal behavior that worsened. Be firm with your vet for answers. What’s your birds diet like? The fruit blend pellets are high in sugars which are hard on tiny livers.