Aeration devices are best suited for shallow ponds (8 feet deep or less). They are designed to create a refuge of oxygenated water for fish to survive until environmental conditions improve. These devices provide some limited mixing of waters near the surface. Aerators may be operated on timers, or are activated manually when low dissolved oxygen concentrations are detected or anticipated. For instance, nighttime aeration may be practiced between 10:00 pm and 10:00 am during the warm summer months.

Importantly, a diffused air de-stratification system is not a substitute for pond aeration. If fish are to be heavily stocked and fed, the installation of an emergency aeration device should be considered. Alternatively, a diffused air system should provide better water column mixing in deeper ponds than would an aerator. Certain pond management scenarios may benefit from the use of both systems.

Most de-stratification and aeration devices are powered by electricity. In some instances, the cost of pond-side electrical installation may be prohibitive. Wind, solar and diesel-powered devices are available as alternatives. However, it is unlikely that wind or solar energy will provide enough energy to effectively or consistently provide improved water quality.

Diffused air, de-stratification systems are typically powered by electric air compressors or blowers located near the pond bank. A submerged air hose connects the air source to a series of diffuser grids made of air stones or porous hose. Diffuser grids have a plate, tray or other device that allows placement near, but not directly on the pond bottom. Here they can release air bubbles that rise to the waters surface unobstructed by bottom mud, plants and organic debris

Pond diffuser systems work primarily by promoting movement of deeper water to the surface creating a constant mixing or de-stratifying effect approximately every 24 hours. Secondly, some oxygen is transferred into the water column as the air bubbles rise to the surface. By keeping the pond waters constantly mixed, a diffused air system may prevent low dissolved oxygen emergencies from occurring, but will do little to correct such an event once it is in progress. These systems are generally run continuously during the warm weather months and may be operated during the winter months to prevent ponds from completely freezing. Diffused air systems may be removed and cleaned during late fall and re-installed in spring before pond stratification occurs.

systems may be removed and cleaned during late fall and re-installed in spring before pond stratification occurs.

Oxygen transfer efficiency increases with pond depth and the amount of contact time the air bubbles have with the water column. With the proper compressor, these systems tend to be more efficient in deeper water (greater than 8 feet) than in shallow ponds. Diffusers stones or hoses are made of fine-, medium-, and course-pore material. Fine-pore diffusers release smaller bubbles that have more surface area and transfer oxygen more efficiently to the surrounding water. However, smaller bubbles create less vertical mixing of water as they rise to the surface than larger bubbles. Fine pore devices must be injected with greater air pressure and will clog more frequently than those made of more course material. Course-pore diffusers may be used under lower air pressure and will allow more vertical water movement to the surface. However, the larger bubbles will transfer less oxygen into the water. A medium-pore air diffuser system should be adequate for most pond applications. A large, shallow pond would require more diffusers to be placed on the pond bottom to effectively mix the water column. Alternatively, a deeper pond of similar surface area could use a less powerful compressor to deliver bubbles with greater contact time from fewer diffusers. Diffused air system manufacturers should be consulted regarding the appropriate type and size system to install in a specific pond.

One advantage of a diffused air system is that there is no electrical device in the water which avoids a potential shock hazard. The compressor may be located away from the pond bank. A disadvantage of these devices is the power units tend to be noisy. They are best housed in an insulated enclosure with plenty of ventilation for

the air intake. System diffusers and air lines will require periodic cleaning. Air filters will require cleaning or replacement.

Solar and wind powered diffuser systems are available for ponds without access to electricity. However, solar panels must provide enough energy to pump adequate amounts of air into the water to provide effective pond de-stratification during daylight. During nighttime