The pump running your biological filter must run continuously, supplying oxygenated water to the bacteria working in your filter.
Pumping minimum 1/2 pond volume through bio-filter per hour. Aeration (such as waterfall) helps bio-filtration by raising oxygen levels in your pond and is beneficial to your fish as well.
Debris and Algae
Accumulation of too much debris( dead leaves, vegetation, etc) in your pond and/or too much filamentous (string) algae will tend to plug up your pump causing a restriction in water flow and bio-filtration, not to mention excessive wear on your pump.
Try putting your pump in a mesh basket with at least a 1" clearance between pump and basket (1/4" mesh works fine) to hold back debris and algae - also raise it up off pond bottom- your pump will need cleaning less often.
Regular use of a bacteria supplement such as Bacta Pur "Klear" and Bacta Pur "SludgeBuster" will keep your pond bottom clear of dead vegetation and sludge build up and help keep filamentous algae under control by boosting the concentration of beneficial bacteria colonies that already exist in your pond and filter. It is this bacteria that decomposes the dead plant material and fish waste. Your filter will also run longer between cleanings.
Only clean a bio-filter when water clarity suffers, or flow from filter drops.
New bio-filters take longer to become fully activated, while they build up bacteria colonies to eat up the nitrites and ammonia which cause algae bloom (green water). How long your filter runs between cleanings and water clarity depends on:
To clean a bio-filter, use nothing but water - a strong stream from a garden hose and some patience works well. Rinse out as much as you can and re-assemble.
We recommend covering your pond in the fall with netting to keep out falling leaves. Cutting back your pond plants keeps as much dead vegetation out of your pond as possible. As vegetation decays over the winter, it will use up oxygen your "pond pets" need. While a few leaves won't hurt, enough can be lethal, depending on your fish to pond size ratio. Many ponders use an air pump to keep a hole open in the ice and to constantly put fresh air into their pond and allow bad gases to escape. Some use a pond heater on a timer, or only plug it in during severely cold periods. These heaters can consume a lot of electricity if left on for long periods Although opinions vary about cleaning, drying and storing a bio-filter over winter , we recommend this, but as with most ponding techniques, whatever works for you is all that matters