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Wednesday, March 21, 2012

Exploding Filters

Exploding Filters

All types of swimming pool filters operate under pressure.  If air is trapped in the filter and not released the air will continue to compress while the filter is operating.  Small amounts of air can work its way out of the filter but large amounts will compress to a dangerous level.  When this occurs the filter may blow apart.  Also, if a retaining ring is not seated properly or if the tightening band fails this can happen.  Pressure build up from a filter not being cleaned can also build dangerous pressure.  During pollen season it is imperative to check the filter pressure often. Serious injury and death has occurred from an exploding filter.

Most filters will have an air release mechanism that needs to be opened when the system is turned off and also left open when starting the system until a steady stream of water comes out through the mechanism indicating that the air has been removed from the tank.  It is of the utmost importance to use this feature.

For filters that have a retaining band (clamping) with a bolt that tightens the band it is necessary to be sure the washer remains in place so that the bolt cannot slip and allow the top half of the tank to become a projectile when pressure builds within the unit.  This band and tightening mechanism also needs to be replaced if it has rusted or corroded as it could also be compromised.

With units that are connected with a tightening band or a “posi-lock” band (threaded like a mason- jar ring) it is very important to be sure that no dirt or debris is present in the area where the two halves are connected as this could also cause a failure.  Be sure that the halves are seated properly and fully seated when re-assembling.  Inspect the locking band for hairline cracks or ruptures on a regular basis.

In 2004 a recall was issued by the Consumer Protection Safety commission on some Sta-Rite and Aquatools brand filters.  These filters were manufactured from January 2003 – October 2003.  For more information see: 

When high pressure builds in some filters that are banded or bolted in the middle of the tank a leak may develop from that area due to the high pressure.  If this occurs turn the system off, wait a few minutes and carefully open the air relief valve to allow the pressure to escape.  After the pressure has been let out of the system, start the system up and allow a steady stream of water to escape from the air relief valve before closing it.  Backwash or clean the system as that can cause building pressure as well.

Again, regular inspections can prevent this dangerous situation.

Thursday, March 15, 2012

Vinyl Liner Mold - Black Bottom Stain

Vinyl Liner Mold

A discoloration of a vinyl liner can occur from mold/fungus that may grow under the liner.  This has the appearance of a black stain on the vinyl liner inside the pool.  It us usually round over a large area and is only seen on the bottom and side walls of a vinyl liner where the liner comes in contact with the bottom areas of the pool.  This can occur on the bottoms of above ground pools as well.

It does not brush off and may lighten in appearance after “shocking” the pool or periods of high chlorine residual.  Shocking and use of a copper based algaecide may kill the substance on the swimming side of the vinyl.  Although the mold can be lightened from water chemistry there is no way to treat the source of it on the outside of the vinyl from within the pool.  The mold can only be eradicated when the liner is removed and the ground is sprayed with a sodium hypochlorite solution of 5-10%.  The chlorine solution can be applied with a pressure type garden sprayer.  The solution must dry before re-installing the liner.  There are specific fungus products available on the market as well.

Another indication that vinyl mold/fungus is causing the discoloration is that the welded doubled seams of the liners do not show any discoloration as they are too thick for the mold to grow through.  The heat welding process also inhibits the mold/fungus from growing all the way through the seam.

This mold/fungus thrives in moist ground conditions.   Areas with high water tables or areas that have experienced flooding can be prone to this occurring.  Infected sand that is used for the base of the pool can also contain this mold/fungus.  Water tables can change over time and with environmental conditions and cause mold/fungus to grow when there may not have been a problem before. 

The plasticizers and lubricants used to make the liners are ingested as food for these micro-organisms and allow it to thrive.  The consumption of the plasticizers which make vinyl pliable comprises the liner integrity.  It is common to see this occur in one season.

The liner can be compromised as the pigment of the liner may be removed during the process of the mold growing through it.  This reaction happens when the bond of the ink and the vinyl is weakened and the ink rubs off.  Many liners are manufactured with a biocide/fungicide but it can be overpowered with heavy infection of the mold.

To avoid liner mold/fungus always be sure that the pool base is constructed with clean sand that is free of organic matter.  Be sure the liner you purchase contains a biocide or fungicide.

Chlorine levels of 5ppm usually will “fade” the mold on the inside of the liner.  Over time these areas may look bleached as if someone improperly added chemicals to the pool. 

Polyethylene sheeting can be laid down to act as a barrier between the vinyl and the ground as the mold/fungus cannot penetrate the polyethylene.  However, if water tables rise the sheeting can “float” with the liner and bundle up when the water level retreats.  A ground sealant or other chemicals can be applied but may get diluted by ground water.

Monday, March 5, 2012

Alternative Media for Sand Filters

Alternative Filter Media for Sand Filters

     Zeolite and Glass media were introduced to the swimming pool industry years ago.  At that time little was known about these types of media use in pools although they had been used in other industries for water filtration.  We now know much more and can make an educated decision if either of these are a choice we want to consider in our pools filtration system.

     The removal of particles during filtration and the efficiency of the media are very important.  With all of us attempting to be water conservative and energy efficient it is time to again look at these alternatives.

     A media that has steadily gained customers is Zeolite.  Zeolites can be natural or synthesized.   Zeolite is a honey combed shaped structure with a surface area 100 times greater than sand.  With the increase in surface area the filter is capable of collecting more dirt in a shorter period of filtration time which enables a decrease in how long you need to run your filter.  

     Zeolite will filter out particles down to 2 – 5 microns which is comparable to diatomaceous earth filters.  This increase of efficiency also increases removal of wastes, algae and gives superior water clarity without the expense of purchasing a new DE type filter.  Due to its low micron removable there is no need to use a clarifier while using Zeolite.

    Zeolite has the ability to absorb ammonium compounds that are created by swimmer waste.  Traditional sand filters do not have this ability.  By removing the ammonia compounds there is less frequency with having to “shock” the pool, eliminates red burning eyes by reducing the chloramines in the water.  This saves on the amount of chemicals you must add to the pool and saves money.

     Less dense in bulk weight than silica sand, Zeolite is used at the rate of half that of sand.  For every 50lbs. of sand you would use 25lbs. – 30lbs. of Zeolite.  It has the same life expectancy as sand which is 7 – 15 years.  You can “refresh” the Zeolite by soaking the media while in the filter in a 10% salt solution overnight.   This process is recommended every 2 years.  This still needs to be done with a “salt” type pool as the normal pool concentration is not high enough to properly refresh the Zeolite.

     There is an increase of 2 times the duration between backwashing over sand media filters.  Also the time to backwash the filter is cut by half.  This saves water and also the chemicals that have been used to treat the water.  When it is time to change the Zeolite media you can safely recycle it into the soil as it is an excellent soil additive or dispose of as a non hazardous waste unlike DE.   There is no hazardous dust to be inhaled with Zeolite as there is with diatomaceous earth. 

     On the initial addition of Zeolite there is a need to backwash 3 times with a short period of time between the backwashes to allow the Zeolite to settle.  This does waste some water but the benefits later outweigh this drawback.

     Another type of sand media replacement is crushed glass.  Although available in the states for some time it is more prevalent in Europe.  A study done for CWC which is a non-profit organization that provides recycling marketing services to business and government has documented that using glass media improves water clarity by 25% over sand media, increased the backwash efficiency by 23% and 20% less media was needed over sand media.

     With the increase of water clarity the filter run times can be decreased to achieve the same clarity of water.  The amount of time necessary to backwash the filter was decreased saving chemical treated and heated water.  Both of these save energy costs as well. 

     The glass particles used have the shape required to be able to remove particulates but are smoother than sand so that it is less likely to support algae growth.   The surface of the glass is negatively charged and attracts iron and manganese to it.  There is no silica hazard as with sand as well.  It works well with “salt water pools”.   It lasts 3 times longer than sand media with a 5 year minimum life.

     Glass media is not as readily available as Zeolite or silica sand at this time.  In discussion with distributors of this product there has been some objection by consumers to use this as the thought of glass entering the pool through a broken filter lateral would not be desirable.  Hopefully we can gather more information on this product and actual use in the future.

     Through the use of alternative filter media we can increase the clarity of our swimming pool water making them more inviting than ever without the use of more chemicals.  We can also make them “green” by saving energy as well.  You can make your neighbors “green” with envy on your beautiful pool with little effort or money.

Resources used:

“Evaluation of Recycled Crushed Glass Sand Media For High- Rate Sand Filtration”

CWC  October 1998

Zeo : Natural Zeolite Products web page (

Friday, March 2, 2012

Get Horizontal!

Horizontal High Rate Filtration

     A common type of filtration for all swimming pools for the past 35 years has been a vertical high rate sand filter.  But now we have horizontal high rate sand filters available that can increase energy efficiency and supply the filtration that is needed.

     Vertical high rate filters are limited to lower flow rate capability (gallons per minute)  as the filter area is small and the flow rate per square foot for applications can only go to 20 gpm/sq. ft.  A large vertical filter tank that is commonly used only has about 7 sq. ft.  Our industry uses vertical high rate sand filters in tandem for large pool volumes or where higher turnover rates are required.  This also demands more plumbing and control which increases the resistance or total dynamic head of the system.  When we increase the TDH in a system we need more energy to achieve the required gallons per minute of flow.  Depending on the need, this can also require more space to install the system.

     Horizontal filter tanks increase the flow media area available dramatically.  It is common for these types of filters to have 27 sq. ft. of filter area. This enables a system to provide more gallon per minute flow and increase turnover time.  Many of these filters are NSF (National Sanitation Foundation) approved for flow rate per sq. ft. down to 5gpm /per sq. ft. instead of 20 gpm/per sq. ft.  At 20gpm a horizontal filter at 27 sq. ft. of filter area would allow 540 gallons per minute of filtration as opposed to 140 gallons per minute in a 7 sq. ft. area filter. They can be installed in tandem for large pools as well but would require less tanks, plumbing and controls which would lower our energy (pump) requirements as there is less resistance. (TDH)  Automatic backwashing controls can be installed on these filters.  

     Ease of use, better cleaning and lower costs to install and maintain without the compromise of water quality make this type of filter an excellent choice for aquatic facilities and other commercial pools.