The importance of Pond Water “Oxygen Levels”
Pond Keepers argue ferociously about pond Oxygen levels. Some say oxygen levels are “always safe” in ponds with waterfalls and fountains, while others don’t regard fountains or waterfalls as effective aerators.
Either way, oxygen levels are very important. If the oxygen level is chronically low (for example, 5.0 ppm), the fish will grow much more slowly, they’ll get sick easier, and they may even die.
If the oxygen levels are much too low on the short term (for example 3.0-4.0 ppm), the fish will gasp or pipe at the water’s surface and they will die.
Large fish die first when oxygen levels are too low because large fish demand more oxygen to live. When the first fish dies, its body begins to break down and the decay process increases the oxygen demand of the pond even more, causing a rapid avalanche of fish losses.
Always bear in mind that warmer water (78+) carries MUCH LESS oxygen than cold water (68*). Oxygen problems are VERY common in summertime while the water is warm.
To make it worse, submerged plants and algae consume oxygen at night or in the dark. Submerged plants produce oxygen in light, or in the daytime. Plus, in warmer water the metabolism of your fish and all the bacteria (good & bad) is at its peak using much more oxygen.
Pond depth influences oxygen levels as much as temperature does. Oxygen-penetration down to five feet of water is difficult. If your pond is more than four feet deep, you will need to put a pump on the pond bottom in summer, to push the deep water to the surface for oxygenation.
Waterfalls and fountains will not aerate “deep” water unless the water is physically drawn from the bottom for these features. Oxygen levels at five to six feet may still sag, despite this.
Oxygen levels are testable, with commercial kits, or have someone test the oxygen levels for you. Assess a warmer, deeper pond much more scrupulously for oxygen problems.
Excerpts in this article were taken from Pond Crisis an Aqua Meds website.