What is Oxygen?

Oxygen is required by all living organisms in order to breathe. Fish, plantlife, algae, and bacteria, they all need oxygen to function. Nitrifying bacteria use oxygen in breaking down organic waste. So, as you can see, oxygen is an essential component in the life cycle.

Oxygen is introduced into the aquarium via two ways:

1. Diffusion - Oxygen enters the aquarium at the water surface. This oxygen exchange at the water surface can be increased through agitation/aeration of the water surface (water movement). This is often achieved through bubble wands, air pumps, filter outlet valves, and basically any equipment that will increase water surface agitation.
2. Photosynthesis - Plantlife uses sunlight and carbon dioxide in the photosynthesis process and produce oxygen as a by-product. Note that plants also use up oxygen for their own respiration, but the total oxygen output provided by photosynthesis far exceeds the oxygen consumed by plants through respiration.

If your fish are gasping at the surface of the water, a likely cause may be a lack of dissolved oxygen in your aquarium. Factors which will lower the amount of available oxygen in your home aquarium are:

• insufficient or non-existent water surface agitation/aeration
• overstocking, a heavy bio-load demands more oxygen
• inadequate lighting in planted tanks
• high temperatures, warmer waters have lower levels of oxygen