(b) A person keeps small fish in a glass container called an aquarium.
The diagram shows an aquarium.
aquarium
aerator
He follows these steps to try and keep his fish healthy.
place the aquarium near a window
use the aerator for one hour each day
set the aerator to pump large bubbles of air rather than small bubbles
feed the fish several times a day with large amounts of food
change the water in the aquarium every four Kays
He measures the changes in oxygen concentration in the aquarium water over a period of four days.
The graph shows these changes in oxygen concentration.
The person claims he keeps his fish in good conditions. Evaluate this claim.