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How to Service Pressurized Koi Pond Filters

Pressurized filters (Mechanical) for koi ponds have been around for a long time. Even though they are highly effective when used alongside a biological filter, long term service beyond weekly backwashing is needed.

Almost all koi pond manufactures sell external pressurized filters for the industry.  Aside from their minor differences in design, they all attempt to accomplish the same two goals. That is to, under pressure, trap the pond waters solid waste in the filter media and provide an environment for beneficial bacteria to live on the media beads. They can be highly effective when used with a biological filter. Very often however, they are the only filter for a pond.

Pressurized Filters Various SizesBio-Media Filter Beads
Pressurized FilterUltima II Beads

The great advantage of a pressurized (also called mechanical) filter is the capability of mechanically backwashing the filter media when it gets dirty. When the valve is turned into the backwash position, it reverses the water flow and the beads inside the filter are churned up and the waste is washed out into the drain while the beads remain intact. 

Years ago, koi keepers relied on converted sand filters to do the filtering (which looks very similar to a bead filter). Because of its fine filtering, this type of filter is used primarily in the swimming pool industry.  It requires a 1-3 hp high-speed pool pump to “push” the water through the sand. Since koi keepers like to run their systems 24/7 to provide oxygen for the fish, the energy costs can be enormous.  Although this filtration method keeps the pond very clear for a while, the media becomes clogged and compacted very quickly. To help keep the sand loose, the filter must be opened by removing the backwash valve to expose the sand/gravel and “stirring” it with a shovel. Also, since the weekly backwashing isn’t enough to remove all the dirt, the media must be removed and replaced yearly.  This is a costly, dirty and labor-intensive chore.  As a result, the pond industry recognized the need for a more practical and energy efficient approach. Hence, the beaded filter was designed. Using plastic beads as the filtering media, the pump needed far less pressure to move through the media. So, more efficient, lower h/p pumps is all that is required. In fact, with high pressure pumps the water simply "blows by" the beads and filtering becomes ineffective. Also, the lower pressure allows for beneficial bacteria to live on the beads, hence "killing two birds with one stone" by both filtering the water and providing a healthy biological environment before returning to the pond.

To understand how a pressurized filter operates, please refer to the diagram below:

Sideview of FilterFilter Positions
Ultima Filter SideviewBackwash Valve

As you can see by the left diagram, water comes from the pump to supply the filter. The valve has 7 positions to choose from.  Each position performs a different function which is listed below.

  • Filter:  Provides normal filtration of pond
  • Backwards:  Reverses flow for cleaning filter. Operates jets
  • Rinse:  For cleaning residual backwash water and re-setting filter bed
  • Re-circluate:  For bypassing filter but recirculating water in pond
  • Waste:  For lowering pond level/draining
  • Winter:  This position leaves the ports open in freezing weather to prevent water freezing in the filter
  • Closed:  Shuts off flow from pump

The pump must be off when rotating the backwash valve or the pump pressure could damage an “O” ring.  Always rotate the valve clockwise when backwashing.

When the unit is in normal filtering mode, the top lever is positioned in the “Filter” position. In this position, the water is flowing downward through the beads.  When the gauge reads 10 lbs. over the previous backwashing session, this is an indication that backwashing is needed.  The top of the valve image on the right shows the valve in the “Backwash” position. Here, the flow is reversed, flowing upward churning the beads and throwing the dirty water out to the drain. The valve has a small clear sight glass which shows the dirty water passing through when backwashing. When the sight glaass water becomes clear, backwashing is complete. In the filter, water above the beads is still dirty. Rotate the valve (pump off) to the “rinse” position. Rinse for about 30 second until the sight shows clear again. Keep in mind, when backwashing, especially small ponds, the water used for this procedure will lower the pond level possibly below the skimmer intake.  This will draw in air and the pump could lose prime.  After rinsing, return to the “filter” position and resume normal filtering. If the pond has enough water to perform additional backwash cycles, by all means, this is recommended.

 PROCEDURES FOR COMPLETE FILTER CLEAN OUT

If a pond produces a lot of waste, it will tax the filter beads.  Even if regular backwashing takes place throughout the year, the bottom part of the filter will become compacted.  While servicing many of my accounts, I would often take off the valve to inspect the condition of the beads. Reaching down to the bottom reveals if the beads need to be “stirred up” to break up the compaction. If this is not done from time to time and the beads get too dirty, then they need to be removed, washed out, and replaced again.  If this is the case, follow the instructions below for the procedure.

To better understand the elements of a filter, review the following diagram:

Ultima Filter Breakdown

Besides the media beads, the filter consists just a few non-moving parts. From bottom to top are:

  • Hub – It is the base which sits on the bottom and is connected by the laterals and center tube
  • Laterals – Connects to the hub and fold up or are detachable for removal from filter
  • Center Tube – Permanently attached to the hub 

Removing and washing the beads is a simple procedure although it can be a dirty job.  Using long gloves and waders is suggested. Although not mandatory, using a wet/dry vacuum makes the job easier. 

To clean the filter, follow these steps:

  1. Remove the bottom outside drain plug to allow water to drain out
  2.  Unscrew backwash valve fittings with large channel locks
  3.  Unfasten nuts on 2-part retainer ring on valve and remove
  4.  Open the backwash valve to expose the center tube and filter beads
  5.  Plug the center tube with a rag to prevent beads from entering
  6.  Remove all the dirty beads and excess water with the wet/dry vacuum
  7.  Empty bead & water in the vac into a large trash can
  8.  Pull out the center tube to access the laterals and remove by unscrewing
  9.  Remove center tube and hub
  10.  Wash out inside of the filter and vacuum out any excess water
  11.  Wash the tube/hub and thoroughly clean the laterals “slits” with a brush
  12.  Wash the beads thoroughly in the trash can
  13.  Place the center tube/hub back into the filter
  14.  Screw the laterals into the hub and lay them flat on bottom of filter
  15.  Replace the clean beads back into filter (careful not to drop any)
  16.  Replace the backwash valve making sure it fits squarely on center tube
  17.  Re-attach retainer ring with screws and nuts
  18.  Tighten all fittings and restart pump
  19. Check for leaks on all positions of backwash valve

After restarting, the pressure on the filter gauge should read 12 lbs. or less. The water flow should now be at its fullest and clarity should improve with 24 hours.

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