LikeLion 09015 Pond Skimmer nets-6" Standard Debris Net,for Aquascape Large Mechanical Classic Pond,Replacement for Aquascape Classic Series Skimmer

The hole in the skimmer box under that yellow hose is for overflow. Keep the water level below that. I recommend running a buried water line into the skimmer box and controlled by a float valve in the box. This will keep the level constant. You also need a skimmer net in the box. Wish I could post a picture of mine. https://a.co/d/07ZfcmUy