The gravel can be laid down after the sides have been cleaned. You can use a siphon to suction dirt and other muck off of the gravel.
Keep at least half the tank's water at all times so that you don't have to worry about losing the tank's beneficial bacteria.
Additionally, the siphon can be used to drain some of the tank's soiled water.
Fill the tank with fresh water once you've finished cleaning it.
In no other circumstance should water be added to the aquarium other than this one.
Be sure to use a conditioning treatment to get rid of the chlorine in the water before adding it to the tank.
There will come a time when you will wish to clean your plants, pebbles, and other decorative items because of obvious dirt buildup.
It is safe to put them back in the aquarium after they have been cleaned.
Take these things out of the tank and give them a good washing in running water or soak them in water overnight.
Are Turtles Lucky or Unlucky?