I would like to know which of these filters would suit me best. The choice is between Laguna PowerFlo 4500 External Biological or Matala Biosteps 10 Pond Filter. This would be an add-on to the Laguna Pressure Flo Clean 1400 Filter I am presently using. The pond is approximately 800 gals with four kois at about 6".I just want to have added filtration for the pond. Here is a photo of my pond.