Then, if needed, you can adjust the pH with chemicals also from the pet store. Just be sure to follow the instructions carefully. Often, good aeration and filtration, together with good housekeeping, will eliminate the need for any chemical adjustment of your tank's pH. Dissolved Oxygen Just like you and I, our fish need gaseous oxygen to live. They can't breathe the oxygen that's bound with hydrogen to make water. Water absorbs gaseous oxygen from the air at the water's surface and turbulence increases this absorption.
Healthy plants give off oxygen during photosynthesis.
However, photosynthesis occurs only when plants receive enough light. At night, or when the aquarium lights are off, plants consume oxygen during respiration. Therefore, an aquarist shouldn't depend on plants as an oxygen source. In fact, unhealthy plants increase the oxygen demand in an aquarium. Microorganisms that decompose dead and dying plant parts consume oxygen.