Yes, decorative fountain pumps can be used in ponds, but there are several considerations to ensure they function effectively and safely. 
Firstly, the pump's capacity should match the pond's size. A pump that is too small may not circulate the water adequately, leading to stagnant water and potential algae growth. Conversely, a pump that is too powerful can create excessive turbulence, disturbing plants and aquatic life.
Secondly, the pump should be suitable for outdoor use and submersible, as it will be placed underwater. It should have a durable, weather-resistant casing to withstand environmental conditions.
Thirdly, consider the pump's energy efficiency. Since pond pumps often run continuously, an energy-efficient model can save on electricity costs over time.
Additionally, the pump should have a filtration system to prevent debris from clogging it. This is particularly important in ponds with fish or plants, as organic matter can accumulate quickly.
The pump's noise level is another factor. While some people enjoy the sound of water, a noisy pump can be disruptive. Look for models designed to operate quietly.
Finally, ensure the pump's fountain head is adjustable to control the water flow and pattern. This allows for customization of the fountain's appearance and helps manage water aeration, which is beneficial for pond health.
In summary, while decorative fountain pumps can be used in ponds, selecting the right pump involves considering the pond's size, the pump's capacity, energy efficiency, durability, noise level, and filtration capabilities. Proper installation and maintenance are also crucial to ensure the pump's longevity and the pond's ecological balance.