It dissolves in water from the atmosphere and is produced during photosynthesis of water plants. Oxygen is removed from water as bacteria decompose organic materials. Temperature is important to water because gases dissolve better in cold water than warm. Oxygen levels will drop as water warms up. The rate of photosynthesis and plant growth also increase.
Metabolic rates increase in warm water and even more oxygen is needed.
Goggles should be worn when using acids or bases. To learn how water is tested and what the tests indicate. Follow the directions on the kit. To test pH, get the water in your beaker. Dip the litmus paper in the water and compare it to the scale.