My pond was 1,500 gallons, roughly 13X8 and 28" deep. I bought it as a package deal. BUT it took me about a year and a half to realize that the filter that was included was undersized!!!
And not by a little.
Eventually I had a separate pump to filter water through a U.V. Light enclosed inside a plastic housing. The uv light took care of all of the parasites. Like I said, I lost 2 fish in 35 years. If you don't have one, you are just shoveling you know what against the tide!!
Then I had another larger pump circulate the water through a box filter. It had a compartment with three upright foam inserts. One was coarser then the two finer ones. Then another compartment had red lava rock in a compartment that was 16"x 10"x 8" deep to the best of my recollection. These materials worked together. Beneficial organisms colonized every surface aiding in keeping everything clean. A biological filter is what I called it.
Every spring upon start up, the filters took about a week to make the water crystal clear. I could tell if a dime sitting on the bottom was heads or tails!!! When the pond was running full swing in the summer, I had to clean the box filter (lava rock and sponge) once every week to ten days.
Now this is KEY, with the undersized filter box, I had to clean it almost every day!!!
I can just about guarantee you 110% that if you are having fish deaths due to parasites or whatever, it is because of water filtration. No doubt in my mind!!!!
My fish capacity was about 15 Koi, about 150" worth. I had long tailed and regular comets in there, about 3 dozen or so for about another 125" worth.
