Best UV sterilizer and DIY FIlter for 1500G?

[cinfid12]

I have a pond around 1500G I am guessing I made last year. It doesnt have a filter and I have a 9W Tetra UV 1 uv sterilizer. Im not sure if thats enough and I would like to make a DIY filter to save some money.
I want a filter that will keep my pond as clean as possible that I can back flush so cleaning is easy. I will be getting koi. Help is appreciated
Thanks!

Also to prevent hair algae what is the best method? I've heard of Barley if I had to I would use algae killer.

 

[27goldfish]

As for the first question, go from your pump to the uv and then to your filter. You have a few options. You could do the 55 gallon filter. Believe it's either a doc or skippy. Not sure. As far as algae, do you mean string algae?