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Diatomaceous earth (DE) filter  

A DE filter has several porous fabric covered elements internally. The elements are also known as grids or panels.  They are simply a thin plastic 'skeleton' covered with a special fabric.  The elements fit into a manifold that holds all of them securely in place. The configuration allows water to flow through the elements and manifold, then leave the filter tank. The term 'diatomaceous earth', DE for short, relates to the white powder that must be added to the filter for the filter to work properly.  DE is crushed skeletal remains of tiny diatoms that once lived in the oceans.  The DE is mined from the ocean floor, cleaned, crushed even finer than it already was, and packaged for, among other things, swimming pool filters. DE is a very sharp particle on a microscopic level.  With good physical characteristics like that, it stands to reason why it is used in filtration.  The powder is sent to the filter, in proper amounts, through the pool skimmer with the pump running and the backwash valve set to 'filter'.  The powder then self-deposits itself on the outside of the fabric filter elements in a thin layer called the filter cake. The element fabric is porous, but does not have large enough openings to allow the DE to pass through.  The DE actually closes the porosity even more, while still allowing excellent water flow through.  This condition allows for trapping particles measuring as small as 2 microns.  That is pretty much microscopic. It would take 500 of these particles lined up side-by-side to be the length of 1 millimeter.  Your pool will sparkle with clarity as the water passes through the DE filter cake, depositing debris on the cake, and then re-enters the pool.  You can tell it's working by watching the filter pressure gauge as the days and weeks go by.  The pressure will increase as the trappings in the filter increase.  At the point of when the pressure is about 10 psi higher than when the filter is clean, it's time to backwash. When the filter is backwashed, water is diverted from the backwash valve in reverse direction through the filter elements.  The backward flow of water flushes the DE filter cake off of the elements and discharges the dislodged DE and debris from the filter.  The backwash flow of water almost completely renews the filter elements.  After re-setting the backwash valve to 'filter', you will have to install fresh DE each and every time you perform a backwash.  The pump will have to be running to deliver the powder through the skimmer.  Use about 1 pound of DE per 10 square feet of filter area, (see the label on the filter for

sizing).  Never run your DE filter for more than a few minutes without properly installing DE.  You don't want dirt and debris to impact on the filter element fabric, since that will damage it prematurely.  DE elements may likely last 5 to 7 years when sized and maintained properly.

Backwash variations  

There are a few notable points of interest for safely backwashing a sand or DE filter that will need to be identified by the pool operator.  Some conditions apply only to DE filters, and some conditions apply to DE and sand filters.  Here are a few things to look for:

Sand and DE filters 

Visually trace the waste water plumbing line as it leaves the backwash valve or multiport valve.  On many waste lines, very near the backwash valve (or multiport), a 'sight glass' is installed by the plumber or manufacturer of the valve.  The sight glass is simply a clear glass pipe section, or a clear bubble that allows you to see into the plumbing line.  Try to locate your sight glass.  Hopefully you will have one, as you will soon see why.  First, the sight glass allows you to visually monitor the clarity, (or dirtiness), of the backwash water during that cycle.  That will inform you of the proper time to discontinue the backwash cycle - when the water runs clear.  Secondly,

it distinguishes the backwash waste line for easy identification.  You really need to know where the water is going once it leaves the filter, so you will know that it won't be blocked by a closed valve, or send the nasty waste water back to the pool.  IF the waste line has a valve on it before continuing to the sewer line, you MUST open the valve prior to backwashing the filter.  Failure to do so will cause a high pressure build-up inside the filter tank, possibly causing a rupture, while the filter is trying to backwash.  If one exists at all, a valve located in this position is just as likely to be found on a sand filter or DE filter.  If yours is a DE filter, be sure to read the next section...

Separation tank and bag

DE filters, a unique possible feature  

Many DE filter systems employ a pool water-saving and environmentally friendly device built into the backwash system.  It's called a 'DE separation tank', and you must be able to identify it, and understand its function and operation.  If the GENERAL INSTRUCTIONS provided here do not make the system perfectly clear and understandable, seek professional advice from a swimming pool technician prior to using the

backwash system:  Look for what appears to be a second cylindrical 'filter-looking-tank'  that is smaller than the main filter (one pipe in, and one pipe out – no motors or wires).  The tank will have a lid with some form of clamp device holding it on - usually a large band clamp.  That is the separation tank. Inside the tank is a filter bag.  It is a bag almost the size of the tank, and it has a fabric handle on it to lift the bag out.  The bag rests snugly on a lip inside the tank, with the top of the bag just under a water inlet to the tank.  Hopefully you have properly identified the separation tank by now, if you even have one in the system.  Do not be concerned if you don't have one.  Your pool is fine without it.  Cautiously follow the waste line plumbing from the backwash valve, (usually exiting the bottom of a backwash valve, and always the line attached to the sight glass bubble on a multiport).  You are going to look for valves that may impede the flow of the filter discharge.  The waste line should lead to the upper part of the separation tank.  From there, pick up the plumbing trail at the lower part of the tank.  The waste line now exits the tank at the bottom, and should lead back to the main pool plumbing system.  It is very possible that the path will be interrupted by one or more valves.  Some valves may lead to by-pass capabilities, (such as to the ground), and others may simply be to prevent water flow from continuing, (these types usually are to prevent water from flowing backward while on 'filter' cycle).  If there are any valves preventing the water from flowing, they MUST be opened prior to backwashing.  Failure to do so could lead to a filter rupture or separation tank rupture due to high

pressure build-up while backwashing.  The by-pass valves are there to do just that; by-pass some part of the system, or send waste water to the ground instead of back to the pool.  By-passing merely defeats the purpose of the water-saving and environmental protection configuration of the separation tank.  When finished with the backwash cycle, be sure to re-set all valves to their original position. Of course, replenish the filter with fresh DE after backwashing.  Also, remove the clamp from the separation tank lid, (with the pump off, until you determine if you can remove it while the pump is running), and remove the bag for cleaning.  Use the garden hose to rinse the bag clean.  Re-set the bag snugly in its place - if it is not placed properly, a lot of debris will return to the pool during the next backwash.  Write on the plumbing lines and valves, if necessary, with a permanent marker for

ease of recognition the next time.  It is suggested to mark all plumbing and valves on the entire system, for ease of use.  The markings will wear off about the time you are very comfortable with

the system anyway.

Separation tank theory  

As the filter discharges dirty water during the backwash, the plumbing

leads the discharge to a secondary smaller filter.  The water passes through the filter bag, depositing virtually all the debris it carries into the bag.  The once dirty, and now clean waste water exits the

separation tank, then travels to the main pool plumbing system, and ultimately finds its way back to the pool.  The pool water is 'recycled' by the pool itself, rather than to be sent to the sewer system, or to the ground.  A typical pool can save literally hundreds of gallons of water per year, during backwash cycles, by using this system.  Think of the chemicals required to treat that amount of

water, too.  Those chemicals are also 'recycled' in that they do not get flushed away to the sewer. This system requires a longer backwash cycle, perhaps twice as long.  Watch your sight glass, or give it a good, long backwash to be sure the filter is clean.

Small clear filter usually associated with RayVac or Polaris 360

And One More Condition Backwashing Some DE Systems

This condition may not exist often, but if your pool is configured this way you'll want to refer to the following picture and description.  That is, some automatic pool cleaners, on the pressure side, may

be plumbed in at the filtration equipment area to receive water flow from an unfiltered plumbing line.  There will probably be a valve to divert the flow of water to the filter or the cleaner directly above, or just exiting the pump.  The valve most likely can be set to allow some water to go both ways in an adjustable ratio.  Again, that valve may be installed prior to the water being filtered. What is vital to know about this arrangement is that if you have a DE filter that needs to be recharged with fresh DE after a backwash cycle, you must close the valve toward the pool cleaner plumbing line.  Remember that when fresh DE is added through the skimmer, you are relying on the pump to deliver it to the filter.  If the water can by-pass the filter in any way, such as going to the pool cleaner line unfiltered, you will see a large cloud of DE shoot back into the pool through the pool cleaner in the pool.  Yuk, what a mess to re-clean!  So, set the valve to send all water through the filter prior to backwashing, and during the recharging of DE to the filter.  The above picture is quite descriptive, if you take the time to follow the plumbing lines exiting the top of the pump. You can see that if the valve just above the pump is set to allow water flow to the pool cleaner, recognizable by the small in-line filter in the clear jar in this picture, the DE would not all make it to the filter.  One more thing; Since this is a popular in-line filter, it is important to note here that its existence does not always mean you will experience the described problem.  The problem only occurs if the valve and in-line filter is prior to the main filter, AND the main filter is a DE filter.