Sometimes it's the best solution especially when there is a strong presence of vegetation, the water is sucked in by a pump through the surface skimmer, rectangular openings on the side walls, and then passes into a filter, then returns into circulation after purification.

This is the most common and familiar system, therefore often also the simplest and least expensive to implement, but it requires a very precise positioning of the skimmers, in this case the only suction system: a casual implementation could cause unpleasant stagnations.