Pond Boss Forums AERATION Systems questions Fountain run times

Firstly. The need or requirement of bottom aeration for just a 6 ft deep pond will depend a lot on water clarity.
Most people do not realize it, don't know about it, or don't accept the fact that most of the dissolved oxygen (DO) in the pond, lake or ocean is produced by algae (phytoplankton, periphyton) and submerged 'greenery'. Atmospheric oxygen does dissolve into the surface water by various ways of moving the water, but those methods do not produce the largest percentage of DO in a water body. Oxygen has a low solubility factor into water thus it dissolves very slowly into the surface water. Thus if the photosynthetic organisms can get enough incident sunlight (euphotic zone 1% of what was at the surface), photosynthetic plants will create DO where they are living. How deep of water they do that depends on water clarity. Read about it or look it up – see more below.

Secondly. Rather than spend a lot of money for a DO meter, I would buy or build a Secchi disk. However deep you can see the disk multiplied times 2 - 2.5 and sometimes 3 depending on the water turbidity, is how deep oxygen is being naturally created in the water body. 3 feet Secchi reading means oxygen is being created at the bottom in 6 ft to sometimes 9 ft of water. When the pond has 2-2.5 ft Secchi, IMO one does not need to have or run the bottom aerator. Fish kills should be very rare unless the water clarity is less than 12”-14". Then there will some concern of fish kill but the likelyhood is still quite rare for a pond just 6 ft or less deep. This because the anoxic no DO zone for a 6 ft depth pond is a small volume compared to the large volume of water in the epilimnion (shallow warm oxygenated layer). Thus the degration factor of anoxic water into the good water is quite low.

Thirdly. Normally when the pond receives “decent” regular wind exposure the wind action will naturally and regularlly mix good quality surface water down to around 6 feet deep, at least that occurs on all the ponds that I measure DO. Buy a DO meter and prove me wrong.

Fourthly. If you have an operational fountain (1hp) , that fountain by itself will adequately mix the upper water layer at least 1 foot deeper that the motor intake. Fountains do not mix water throughout large areas; normally the highly oxygenated zone is mainly in the vicinity of the fountain. Fountains mix their active water over and over dissolving more and more DO in the same water again and again near the fountain. Thus fountains create an area of high oxygen refuge in the vicinity of the fountain. Wind action does move aerated fountain water around into other areas of the pond. A shallow 6ft deep pond with a functional fountain and good wind action IMO should not need a bottom aerator. Wind action should easily in most cases mix oxygenated water down to around 6 ft deep. If you do not use supplemental water to keep the pond at full capacity, during dry, low rain periods with evaporation with some normal pond leakage, expect the deepest water depth during those periods to be just 4 ft to 5 ft.

Bottom diffusers are not really designed to actually add a lot of DO into the water by the bubbling action. Because A. Oxygen dissolves very slowly from inside the bubble into the water. B. Bubbles rise about 1 ft per second. Thus the bubbles are not in contact with the water long enough to get very much oxygen into the water. C. Bottom diffusers are designed to move lots of water cheaply by air lift technology to the surface from the bottom where the lower quality DO water gets degassed and re-oxygenated by mainly the phytoplankton surface zone activity.

IMO - With a pond only 6 ft deep you will have many, many more problems with weeds and algae than problems with low oxygen.

From the Internet
The Euphotic Zone
• Definition: The depth at which approximately 1% of surface light remains.
• Significance: It is the region where plants and algae can produce more energy via photosynthesis than they consume through respiration.
• Depth: In clear open ocean, it can reach up to 200 meters (656 feet), but in turbid lakes or estuaries, it may be only a few meters deep.

The Secchi Disk
• Function: It measures water clarity by determining the "Secchi depth"—the exact point where the disk disappears from view when lowered into the water.
• Usage: It is widely used by researchers and citizen scientists to monitor water quality, as lower Secchi depths often indicate high levels of algae (eutrophication) or suspended sediments.
• Procedure: To get an accurate reading, the disk is lowered until it vanishes, then raised until it reappears; the average of these two points is the Secchi depth.
Relationship Between the Two
While they measure different things, Secchi depth is frequently used as a proxy to estimate the euphotic zone depth:
• The "Rule of Thumb": As a general rule, the euphotic zone is estimated to be 2 to 3 times the Secchi depth.


Primary Sources of Dissolved Oxygen
• Photosynthesis (Major Source): Aquatic plants and microscopic algae (phytoplankton) are the primary producers of oxygen in most pond and lake systems. During daylight, these organisms use sunlight, water, and carbon dioxide to produce glucose, releasing oxygen as a byproduct directly into the water. In some productive systems, photosynthesis can account for approximately 89% of total dissolved oxygen revenue.
• Atmospheric Diffusion: Oxygen from the air naturally dissolves into the water's surface to reach equilibrium. This process is significantly enhanced by wind and wave action, which increases the surface area for oxygen to enter the water. In large lakes, atmospheric diffusion is often the main mechanism for oxygenation, though it is less efficient in small ponds sheltered from the wind.
Oxygen diffuses much slower into surface water than it does through air because water is denser, causing more molecular collisions that impede movement; it can be thousands of times slower, with estimates suggesting it might take years for oxygen to diffuse just a few meters in still water, but rapid mixing from wind, waves, and turbulence speeds up the process significantly by increasing surface area and mixing layers.