If the oxygen demand is great in the oxygen-deficient layer, the dissolved oxygen that is present will be rapidly removed from the water. This may result in a fish kill. Signs of Low Oxygen Fish swim at or near the surface. Fish gulp for air. Piping at the surface.
Fish stop feeding.
There is rapid color change in water to brown, black, or grey. The range goes from 0-14, with 7 being neutral. Water that has more free hydrogen ions is acidic, whereas water that has more free hydroxyl ions is basic. Since pH can be affected by chemicals in the water, pH is an important indicator of water that is changing chemically. Water with a pH of 5 is 10X more acidic than water having a pH of 6.