Did you know, during the daylight hours the algae and other aquatic plants (waterlily, lotus, floating plants) provide oxygen to your pond?   This is a benefit to other aquatic creatures, such as fish.  However, in the darkness, these same plants use the oxygen for energy, taking away the oxygen which aquatic creatures.  All aquatic creatures need dissolved oxygen to survive.

It is important to use air pump for the total amount of water in your pond.  For large ponds (10,000 gallons or more) it is best to use multiple diffusers to ensure proper dissolved oxygen levels are maintained throughout the pond.

Fish Behavior in low oxygenated ponds:

Koi breath by pumping water over their gills, this is how they use dissolved oxygen.  Still ponds are void of proper dissolved oxygen, which is evident with fish kills or abnormal fish behavior.

• Have you noticed fish kills when you wake up in the morning or have you noticed fish gasping (piping) at the surface?  This is a sign of low dissolved oxygen.
• If you have a waterfall, have you noticed the fish ‘playing’ in the waterfall? Unfortunately, they are not playing but are trying to survive as the water coming off the waterfall has more oxygen than other areas of the pond.
  • Koi and goldfish need 7.0-9.o ppm dissolved oxygen to thrive and heal.
  • At 5.0 ppm, fish will display behavior they are suffering.  At 3.0 ppm, the fish will die.
    • DO meters are used to measure the DO levels in your pond but it is not necessary to purchase a DO meter. They are expensive and typically not used by most pond owners. Simply observe your fish and test the water quality.  Fish behavior and water quality are very good indicators of poor DO levels.

It is best to use an air pump suitable for your entire body of water.  If the pond is large, using multiple diffusers will keep the water column moving and well oxygenated.

Diffusers are designed for the depth of your pond.  For example, two inch round air stones are not effective when placed in water more than two feet deep.  Why? It is due to the hydrostatic pressure against the stone and the tubing.  Simply stated the air pump cannot overcome the hydrostatic pressure on the air stone.

It is important to read the labels and the user manuals as all diffusers and air pumps, which have different operating requirements.  For example,  if the air pump operating specification state “for depths up to 7 feet and ponds up to 7500 gallons”, this means the diffuser will work up to 7 feet in depth and the air pump will oxygenate 7500 gallons of water.  It does not mean the air pump is too large if your pond is less than 7 feet deep.  It does mean, ponds over 7500 gallons, will not have sufficient dissolved oxygen throughout the pond, therefore additional air pumps and diffusers or air pump system designed for your large pond is essential in providing proper dissolved oxygen levels.

While robust aeration is always best, especially in ponds where fish are suffering,  it can be distracting to those who who prefer the look of still water and do not like the look of moving the water column, which benefits fish and plant health.  If still water is more important, then the pond owner should avoid filling the pond with fish or other aquatic creatures.  All living things needs oxygen….even plants.   Ponds need moving water, even in natural ponds—without proper dissolved oxygen, creatures will die.

Still ponds are breeding grounds for mosquitoes and will produce carbon dioxide and hydrogen sulfide which do not benefit fish or plants.  If the homeowner prefers a still pond during the day, they may want to use a dusk to dawn timer and run the air pump during the evening hours when the oxygen levels fall to their lowest levels.

Can you shut off the air pump? Yes! Dissolved oxygen, does not drop off immediately after the air pump is shut off but it can be a concern, especially in darkness, as plants will take away the oxygen for their survival (energy) which will negatively impact fish in the pond.   While sitting at the pond, it is okay to shut off the air pump to observe the fish—just remember to turn the air pump on when you leave the pond.

When is the best time to run the air pump?  Always running the air pump is best!  It is very important to leave the air pump running during the night and the winter months.     If you want the air pump off during the day, consider a dusk to dawn timer so the air pump runs at night.

Two Major Benefits of Running aeration:

• Reduces muck (decomposed plants, dead fish, fish waste) in your pond.  Muck uses oxygen, so leaving the air pump running keeps the water column moving and allows aerobic bacteria to thrive and reduces the muck–improving water quality and dissolved oxygen levels, year round.
  • If you have noticed a sulfur smell or methane smell from your pond, this odor is due to decaying matter caused by the lack of water movement (which leads to low dissolved oxygen).
• Provides proper oxygen levels for plants and fish.  Moving water increases dissolved oxygen and reduces breeding grounds for mosquitoes.

Personally, we have never experienced negative results with the use of robust aeration.  We have experienced fish kills and death due to low oxygen levels, high ammonia and nitrite levels.   If you have seen a fish suffering from gas bubble disease, it is more likely caused by the nitrite and nitrate levels.  Use a test kit and check the levels then use products such as Seachem Pond Prime to eliminate the problem.

If you do nothing else, remember robust aeration is the most important thing to add to your pond.