Article 37: Annual Pond Care - Cleaning Filters, by Jeff Richardson - Play It Koi

Cleaning filters will vary widely with you water feature, the weather, the amount and type of debris that gets into your pond, the filter types, and how much flow is passing through all of them.  In general, filters need to be maintained throughout the year.  However, a more thorough annual maintenance will be required to clean out accumulated sludge (sometimes more often).  It just depends on your particular water feature and how you find it behaving over the course of one year (make a schedule and stick to it).   NOTE: Dirty filters can raise the head pressure on your pumps reducing water flow (which in turn makes your pond dirtier, faster leading to unhealthy water).

Types of Filters: Although there are many types, they can be broken down into three overall groups.  The first is mechanical filtration.  This separates out large debris from the water using physical barriers such as screens, nets, brushes, mesh and the like to catch the debris and let water pass.  Next is biological filtration.  Water passing through these filters are changed chemically; usually by the action of bacteria (although this can be changed with chemicals as well).  Lastly, there are clarifiers – this removes suspended debris from water or sterilizes and kills life forms suspended in the water using chemicals, very fine mechanical filtration or UV light.

Types of Debris: Like filters, there are many debris types with interchangeable terms; however, they can be broken down into three overall groups.  There is organic debris.  This is both live or dead plant and animal matter and waste commonly referred to as “Muck”.  There is inorganic debris consisting of minerals, clays and sand; commonly referred to as “Silt”.  The last is the mix of the two commonly known as “Sludge”.  Soil is the land version of sludge.  This debris can found floating, be suspended, or sink in water and range in size from large to unable to be seen with the naked eye.  The different filters, chemicals or biologics target each of these debris types.  The capacity and type of filtration will be based on the type of debris load of your water feature and overall volume of water to be cleaned.

Mitigating Debris: Your water feature will get dirty over time – period; how much and how fast depends on how well your filtration is AND how to prevent it getting dirty in the first place.   First, keep debris out!  Plant non-shedding plants around your pond.  Ensure that runoff and soil do not wash into the feature.  Inevitably, debris will get into the water and produced within.  Use one or more skimmers to ensure that the debris is quickly removed before it becomes waterlogged and sinks (this is harder to clean).  If you see large sunken debris, remove it with a hand held aquatic rake, net or skimmer.  If you see a collection of sludge on the bottom or in your feature, vacuum it up.  Use cleaners that attack sludge to help breakdown accumulated matter.  Further, boost bacteria on a regular cycle to reduce muck as well.  This will slow the dirtying process.  Add clarifiers as needed to clump debris out of suspension.  However, you will eventually have to clean your filters thoroughly to return them to peak operating condition in an annual cycle.

Skimmers: These are designed to catch floating debris and will dirty at a rate equal to the amount of debris falling into your pond.  Skimmers are designed to easily clean them out.  However, once a year, you will need to lower the water below the skimmer weir door and thoroughly rinse and vacuum out the skimmer box to remove any accumulated sludge (more often if you find lots of sludge in the box throughout the year).

Intake Filters: Primer pots usually have a catch basket before a pump to keep debris out.  This is a simple enough to pull out and remove the debris.  However, submersible pumps may need to be taken apart and rinsed as they may have sucked up suspended debris which may have collected in the intake (see the pump’s maintenance instructions).  If you have other intake screens in locations where intake lines remove water from a feature, they will likely need to be rinsed as well.  Dirty intakes will cause greater head pressure on the pump intake side.

Gravel Beds: If you have a large bed of rocks or gravel, you need to clean the sludge from between the rocks.  This is probably the hardest filter to clean.  If you have a pondless water feature, you may have to remove the rocks and spray and flush with a hose then return then to their housing.  If the gravel bed is underwater, use a pond vacuum with a gravel head attachment (which is a large, opaque inverted funnel) and push the head down into the gravel and agitate the rocks.  Debris is loosened and sucked from the rocks.  The vacuum will pull water and debris, but not the rocks themselves due to the width of the gravel head.  Continue in that location until the water inside the funnel runs clear.  Be methodical and perform this at least once a year (or 2-3 times a year if the sludge is excessive).  Too much sludge will reduce water through the filter causing greater head pressure on the pump intake side. 

Biological Filters: The media pads, mesh or balls have living bacteria colonies living on them.  You do NOT want to clean these thoroughly because you will destroy the bacteria.  However, the housings for these containers will likely accumulate sludge.  As this builds up, it will slowly make the filters less efficient.  You will have to remove the media and clean the housings flushing with water and vacuuming away the sludge.  If sludge has gotten into the media itself, you will have to give it a quick rinse just enough to get the sludge off.  If you find that there is lots of sludge overwhelming these filters, you will have to do this more than once a year (perhaps even 2-3 times a year).  Media inundated with sludge will be less effective at chemically cleaning the water.

Clarifying Filters: If you have UV filters, you will need to replace the lamps annually as they weaken or fail over time.  If you have carbon filters to remove staining or suspended debris, these will eventually clog and will need to be rinsed or replaced as well.  Settling tanks are meant to accumulate sludge and will have to be flushed annually.  Again, pay attention how fast these housings for this equipment accumulate sludge to see if you have to do this more than once a year.


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