1. The plastic barrel is mainly sun-baked. When the barrel is exposed to sunlight, the sun's ultraviolet rays are directly exposed into the barrel and directly in the water in the barrel, so the ultraviolet irradiation will be long.
2. The water stays in the barrel for too long (cooked as dead water) and does not flow.
3. Because of the different water quality in different places, the plastic barrels have a long relationship between moss and water quality.