The pump is the heart of the koi pond. It is what keeps the pond flowing and alive. Above we have the pumps sorted by manufacturer. Most manufacturers will have several different types and styles of pumps for different applications. In your review please try and be specific on how the pump was integrated into your system.
There are two basic types of pumps. Submersible and external. Which will work best for you will depend on the size and design of your koi pond. Submersible pumps are usually much easier to install and external pumps tend to be a bit more efficient.
When comparing pumps always factor in watts used vs gallons per hour. Upfront cost can and should play a role in your decision, but don't rule out a more efficient pump because it is more expensive. If it can save you money every month, the cost difference will pay for itself.
You will need to find a balance between what you can afford to purchase, how many GPH you need, how capable you are of installing the pump and what you want your monthly operating costs to be. For more information, please read this article on choosing a pond pump.