It is critical that your pond is initially designed properly with adequate waterflow, aeration and biofiltration to keep the oxygen levels high and the ammonia and nitrite levels low.
Water Flow: As a rule of thumb, you should pass the entire volume of the pond through your filtration system at the very least of once every 2 hours. We recommend once an hour. In regards to the flow, you should have your pump intake at one end of the pond and your water return at the other. Always consider whether a section of the pond will be cut off from the main circulation pattern when you are laying out the pond. If so, you may need to consider adding a small Mag Drive Water Pump or Aeration System to help circulate the water in that section. There is a great deal of pump sizing info on our How to Choose a Pump page. Please note that a common practice is to create a “cut-off” area that will be isolated from cold water temperatures during the winter if the pond owner intends to run their waterfall through the winter. However, these areas usually have their own water pump that can be run during warm weather months and shut down for the winter. See the Wintering Koi article for more on this.
Aeration: You can have the largest waterfall in town, but when (not if) the pump goes out, there is nothing aerating your water. Generally speaking, if a pond has a significant waterfall and the pump runs 24/7, there is usually adequate aeration. However, as stated above, when (not if) the pump goes out, you can be in trouble. Also, ponds with serious algae problems and/or very high densities of fish can still experience low oxygen levels, even with a substantial waterfall. Therefore, we recommend that every pond has an Aeration System installed for supplemental/back-up summer aeration. This same system can also be used for winter aeration if its position in the pond is altered (see Wintering Koi article).
Biofiltration: This is the process where beneficial pond bacteria convert toxic ammonia (a byproduct of fish metabolism and organic decomposition) to nitrite and then nitrate. It does occur naturally, but in most cases there is insufficient surface area for the bacteria to grow. Hence, the creation of the biofilter, which is basically a container that directs water-flow through high surface area media that beneficial bacteria grow on. There are technical ways to determine whether a filter has sufficient capacity, but for your typical pond application, you can just go by the sizing information included with the filter. Be sure the filter is properly sized in both terms of what size pond it will service and whether it will handle the water-flow that is required for your pond. You can visit our Pond Kits page for examples of properly sized pond filters, or consider adding a Water Filter to your existing system.