When you fill the vessel with sand, you must check whether the sieve bottom and the separation plate are correctly inserted.
Before you pour the sand into the vessel, you have to add about 20-30 cm of water to the vessel and slowly fill in the sand to avoid damages caused by the weight of the sand.
Before the first filtering, you must filter the undersize particles of the sand. Backwash for several minutes until clear water comes out of the backwash hose.
Damaged parts such as the sieve bottom or the separation plate must be replaced.