Fishmate (Ani-mate) produce a range of world famous, low cost gravity fish pond filter that are available with an integrated UV and are designed for external pond use.
These external gravity pond filter models are colored green to blend in with the surroundings and fitted with an easy to remove lid for access to filter internals.
Spare Me! Keep a spare air pump or water pump on hand for emergencies. If your pump ever stops, do not feed your Koi.
Consider using seperate water pumps for your waterfall and filter. This way you will always have a backup, and you can save energy.
