l have a 300 Gallon pond with around 15 goldfish. I have had it for 2-3 years. Right now the water is real green and theres algea all around it on the pond. I don't use a filter besides a uv ray light that I just hooked up hoping it will fix the green water. But I have never really did much maintenance to my pond and I want to start keeping up with it better. So should I buy a filter? If so which and what pump? And should I do weekly water changes? And whatever else I need to know just tell me, Thanks.