UV filter

Hi, I’m just trying to work out a set up for a pond that I’ve been left with(around 8/9000L with one large koi, 3/4 very small koi and 5/6 goldfish). Currently, there is an old UV clarifier(I can’t see any glass for a light to indicate that it works), a separate pump(10000L/H) and a DIY filter with sponges and balls which is higher than the pond creating a “waterfall”. I am firstly looking to purchase a uv filter, the water is very green. I’ve seen that a 55w UV clarifier has a 5000L/H capacity. Will that work with the larger flow coming from the pump? Is it better to get a filter with UV already incorporated into the system? Although, I have noticed that in these cases the UV is low with these systems. Any advice would be appreciated! See less