SwimmingPoolsThailand Filtration Guide 

Links to contents:

About filtration
Robots
Disinfection vs Filtration
Sand filters
Multi-port valve: How it works
Cartridge filters
Diatomacious earth (D.E.) filters
Products and further advice pages

Filtration

Swimming pools in the tropics should be filtered completely in a total of about 6 - 8 hours pumping time every 24 hours (Australian and Californian laws for public, school, and commercial pools). Pumps and filters should be matched - a filter should preferably have a slightly higher flow rate than the pump.

Filtration removes small solid particles which remain in suspension in water or which settle on the floor,  such as dust, sand, ash from sugar cane burning, leaves and other vegetation, dead insects, dead algae, and molecules of grease, cosmetics, sun lotion, etc.

Filtration does not remove substances that are dissolved in water such as salt, copper, iron, other metals, calcium carbonate that causes build up of limescale, and most other chemical products, liquids, or urine.

Some microscopic particles are still too small to be entrapped in even the best pool filters. In this case, usually when water is cloudy (new water, dead green algae, etc), you will need to use a flocculant. These clarifying agents are used to remove microscopic suspended solids from liquids by inducing flocculation, causing the solids to form larger lumps that can be easily removed in the filter after they either float to the surface or sink to the bottom of the pool where they can also be vacuumed up or swept up by a pool robot.

Your choice of filter will be based on several factors:

• Your budget

• Cost vs performance

• High, medium, or low average bather load

• Ease of installation

* Your available time for maintenance

• Ease of maintenance

• Cost of maintenance

We look at the three common types of filters: sand, cartridge, and D.E,  with a word about robots. You'll then be able to make an informed decision on what filter is best for you.

Disinfection: Do not confuse filtration with disinfection, they are different processes. Disinfection kills bacteria and algae. It is done by adding chemicals to the water either manually or through mechanical or electronic systems such as ionizers, UV, ozonators, or salt water chlorinators. The most commonly used chemical is chlorine but other oxidisers are also sometimes used. You can read more about disinfection in our POOL DISINFECTION GUIDE.

Robots

A robot does not replace a pool filter. In most cases however, using a high quality robot that works independent of vacuum hoses and the pool pump, can save up to 80% of the manual labour of pool cleaning, and significantly reduces the need for backwashing the pool filter, thus saving water and the environment. The filtration provided by the pleated filter panels is comparable to that of a good cartridge filter. Robots represent a significant investment and are best considered for pools over 40m3 (40,000 litres / 10,000 U.S. gallons) or over 8m long. Read about our Dolphin robots.

Sand filters

A swimming pool sand filter can also be filled with various types of filter media including Zelbrite and crushed glass.

Sand only filters down to about 20 microns, meaning you'll be able to see some of the impurities in your swimming pool water. To put it in perspective, algae is approximately 1.5 to 15 microns. Sand creates sticky clumps and wormholes through which the water can flow without being cleaned. Sand should be changed every three years at the latest irrespective of the bather load. Even if the pool is 'winterised', that is, the pump is not run for several months at a time during yur absence from Thailand, mould and algae can grow i the sand.

Glass is crushed recycled bottle glass and/or industrial offcuts of window glass.  and has much better filtration properties than ordinary silica sand, catching particles down to about 7 microns. Crushed glass lasts longer than sand, often 6 years or even more. It does not clump or build wormholes and it needs less frequent backwashing. A filter needs only 75% glass by weight of sand.

Zelbrite is the best of all media for sand filters. Zelbrite is a clinioptiloite zeolite of a kind found only where it is mined in Werris Creek in New South Wales, Australia. The tiny grains are porous, exposing a huge filtration surface. Filtering down to 3 microns or less, it surpasses the performance even of D.E. filters. The grains are very hard and last for years and Zelbrite can be regenerated. It is so good that it even filters out the ions of silver and copper and that's why we recommend using glass in your filter if you are disinfecting with a ClearBlue ionizer or a Naked Freshwater System. Like glass, Zelbrite needs only 75% by weight of sand.

If you are installing a new filter or refilling with new media, always check that the laterals (the perforated PVC bars in the bottom of the filter tank) are firmly screwed  into the hub of the down pipe, check the state of the O-rings, and fill the filter half full with water before pouring in the media. Backwash and rinse the new media several times thoroughly before setting the multi-port valve on filtration.

Multi-port valve: How it works

The multi-port valve is the heart of your FILTRATION system.

Most Emaux MPV (multi-port valve), sometimes called a diverter valve or a backwash valve have 6 positions: Filtration, Backwash, Rinse, Waste, Recirculation, and Closed (which is rarely used here). They are an integral part of sand fiiters and diatomacious earth (d.E.) filters.

Cartridge filters

Designed for a relatively light bather load typical of home and family pools, modern cartridge filter elements offer a performance close to that of glass filled sand filters with the convenience of sand but very low on maintenance. They are user and environmentally friendly, and due to their small footprint they take up very little space in a pump room making them ideally suitable for folding above ground pools and inflatables. Multi-element units will treat traditional pools up to 250 m³, especially those that do not have a heavy bather load.

Cost

Cartridge filters are the least expensive. The filter element itself represents the largest part of the price of a cartridge filter system. Even taking into account the cost of occasionally changing the filter element, the absence of moving parts and selector valves means they will last a lifetime.

Maintenance

Keeping a cartridge filter in good condition is the easiest of all kinds of filters. There is no backwashing to be done, simply relying on the increase in pressure shown by the pressure gauge is sufficient to know when to remove the element and clean it, but periods between cleaning should not be longer than 6 months. Cared for correctly, a filter element can last for up to 2 years or more.

Advantages & Benefits

Due to needing very little plumbing, the ease of installation is an important consideration. Because they require no backwashing, cartridge filters do not incur a waste of water with the expensive chemicals in it and they are therefore very user and environmentally friendly. There is no need for the use of dangerous substances for regenerating the media and cleaning the element is a simple matter  of using a garden hose with a nozzle at normal household water pressure.

Downsides

To enjoy the full benefit of the low maintenance, it's important to maintain a correct water chemistry in order to avoid attacks of algae or other causes of discoloured or cloudy water. If it becomes necessary to use a flocculant to clarify the water, to avoid clogging the mesh of the paper pleats a product must be used that is specially designed for cartridge and D.E. filters.  After such a treatment, the filter element must be removed and thoroughly cleaned.

Diatomacious Earth (DE.) filters

The filtration properties of diatomacious earth have been known since the antiquity. Nowadays due to advanced designs of low maintenance, high-rate sand filters, special filter media, and efficient cartridge fillers, D.E. pool filters are largely outdated due to their high price and intensive maintenance and costly grid replacement.

Cost

Pool builders and pool stores will recommend them to new customers because they are expensive and make the best profit - and get a captive customer for D.E. powder. Aggressive marketing for years has monopolised the North American market for some brands for so long that even many pool builders often don't realise or bother to understand how much more time saving, water saving, and environmentally friendly sand and cartridge filters are. Compared to all other filtration methods D.E. filters may well be among the most efficient, but are  the most  expensive by a wide margin.

Maintenance

D.E. filters are the messiest and most highly maintenance intensive of any kind of pool filter. They should be disassembled and thoroughly cleaned once a year and the grids inspected for wear and tear and The cost of replacement grids is high. Replacing the grid cloth may be more economical but is very time consuming. 

Cost/Benefit D.E. vs sand, glass, and Zelbrite

The level of filtration provided by sand, about 15 microns, is more than adequate for any domestic pool up to about 100m3 (26,500 gal) that has a light bather load of an average family and a occasional poolside barbecue party. For heavier bather loads, a sand filter filled with Zelbrtte (a "clinoptilolite" zeolite), will not need the media changing for a decade and with its 3 micron filtration surpasses the performance of D.E. Glass media is cheaper than Zelbrite and will also last for many years. Changing normal silica sand every three years is a day's work but far less of a challenge than completely disassembling taking a D.E. filter once a year and putting it all together again. Sand filters cost only a fraction of the price of the D.E. filters which have now largely gone out of fashion outside the US.

Use in commercial and community pools

There may be an argument for using D.E. filters with very big or commercial pools with a heavy bather load where the maintenance budget is not a handicap and  full time staff keeping the pool and its systems running. D.E. powder is a health hazard for the eyes and lungs, ans a carcinogen; people working with it regularly should wear protective clothing and a face mask.

Products and other Info pages

Complete Guide for swimming pool chemicals in Thailand
Flocculants in our online store
About Dolphin robots
Dolphin robots in our online store
Disinfection systems
Water softening systems
Chlorine Guide

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