Article in English: If there are many dead leaves and a lot of sludge at the bottom of the pond that you can't easily remove with a pond vacuum, you'll need to empty the pond entirely.  If you can easily remove debris at the bottom of the pond, a complete cleaning is not necessary. You should empty and deeply clean your pond at least once a year.  The best times to do this are in the spring (so you can remove debris that accumulated during winter) and in the fall (when you're getting ready to winterize your pond). You can buy or rent a water pump from most home improvement stores.  Ensure the pump has a long extended hose or handle so the pump will reach to an appropriate depth in your pond.  To avoid wasting the water, direct it to a garden at the back of your house or to the lawn. Place some of the pond water in a large tub, inflatable swimming pool, or other large container if you have fish.  This water will serve as your holding tank for your fish while the pond is empty. After you've removed most of the water from the pond, transfer your fish to the holding container(s).  The water level should be high enough that the fish can still swim around, but low enough that you can walk easily in it.  Water of about a half-meter in depth is a good level at which to remove the fish.  Remove your fish with a fish net.  Scoop the fish out and place them in the container holding pond water you filled earlier. You might need to place netting or mesh over the container holding the fish to ensure they don't leap out. Once the pond is empty, begin removing the aquatic plants from the pond.  If any of the plants need water to survive, put them in a holding tank.  Scoop up and remove any dead plants or plant material.  Clean the pond while it is empty.  Wash the grime from the bottom and sides of the pond with a pressurized water spray gun.  Don't use bleach or any toxic chemicals on your pond. Fill the pond up with clean water.  Add a dechlorinating agent to the water.  Dechlorinator is a solution designed to remove chlorine from water that...

Summary in Vietnamese:
Tiến hành xả ao khi cần thiết. Bơm nước ra khỏi ao. Chuyển cá ra khỏi ao. Hoàn thành việc xả ao. Bơm nước vào ao.