Sprinkler Filter What Is The Point Of My Pond Filter?

What is the point of my Pond filter? - sprinkler filter

I have 2 pumps in my pond. A pump is to provide to the waterfall. Other pumps to pump water from a hose in a big black box and black box that again) in the pond water (through another tube. This field is a pipe that spans the length of the housing near ceiliing. When the pump is the hose from the roof to spray water into the can. There is another tube that protrudes from the bottom of the box 4-5 cm) to (but below the other pipe on the ceiling. Based on this image of a sponge-like material (2 sheets) is from him. When I see these "filters" in the zone of influence of water, as I mentioned earlier, there is in (pump) for housing through the roof-line (the pipe has small holes for aerosols in the table like a shower ). And once the box is filled with water and reached the portruding drive (5 cm above the ground) and then drains back into the pond.

Now tell me, what is the purpose of this.