Hi need some help if possible, I have an Oase Clear Filter 6000 pressurised unit and 6000 Oase pond pump, I have lived in my house for about 6 years and have never changed the water, you can see on he picture the water is very green. The fish are mating every year at least 30 -50 babies per year. I have 2 Koi as you can see in the picture otherwise the others are all gold fish I think ? I have set up a quarantine tank so I can start to remove some of the babies and smaller fish. What I really would like to know is should I be removing the water and cleaning out the pond from scratch? Bearing in mind this has never been cleaned for at least 10 years. Is there a good time to do this?

I would appreciate any help

Thanks, Steve