Pond filter recommendation

I was wondering if I could get a filter replacement recommendation. ...

I have a 1200 gallon with a small number of Koi and am now using a
TetraPond. Its a gravity system with plastic media and a small sponge on the
top. The water gets cloudy since the filter doesnt filter small particles
from the pond. I do 50% water changes or use polyester floss which works but
is too my maintenance....
Looking to upgrade to a better filter....
Any suggestions are welcome....

Thank you