If you do have tadpoles, sadly, they won't be able to get out when they become juv frogs and will drown; the sides have no slope for them to climb out. Also with 17 goldfish in there they will struggle to make it to juv frogs.
Best time to clear and tend your pond is probably end sept/beg oct. That way any breeding from anything is finished and creatures haven't then started to hibernate. I'd agree that emptying pond prob not a good idea as it will be fairly well established by now.
welcome to the site by the way
