Remove the turtle and decorations: Place the turtle in a secure, temporary container with water, and remove any tank decorations. 2. Use a Vacuum/Siphon: Use an aquarium vacuum, like the Python Aquarium Maintenance System, to clean the substrate and remove the water at the same time. 3. Remove and add water: For a partial change, remove and replace 25-50% of the water; for a full change, nearly all of it. Refill the tank with dechlorinated water of the same temperature to avoid shocking your turtle. 4. Return decorations and turtle: Put back the decorations, and gently return your turtle to its home. 5. Test the water: Use an aquarium water test kit to check parameters like pH and ammonia. Remember that regular water changes and an efficient filtration system are both crucial for a healthy turtle tank.