Are you looking for ways to keep your swimming pool clean and safe? Well, you’re in the right place! Today, we’re discussing the importance of pool filtration and why it’s essential. The article emphasizes on sand filters.
A good pool filter will keep your water clean and clear, and it will extend the life of your pool. There are a few different types of pool filters, but the most important thing is to choose a filter that is the right size for your pool. If your filter is too small, it won’t be able to keep up with the amount of debris that can accumulate in your pool. If the pool filter is too large, it will cause the water to become stagnant leading to poor circulation.
Reasons Why Pool Filtration is Important
The sources of pool contamination are various. Outdoor pools are definitely more exposed than indoor ones. Let’s see the main causes and sources of pool water contaminations:
- Swimmers: Swimmers introduce a good load of contaminants to pool water. These includes, micro-organisms, body secretions (sweat, mucus, etc.), faecal matter and a wide range of cosmetic products such as sun protector oils & lotions, perfumes, etc. It has also been established that each pool user introduces on average 30 to 80 ml of urine in the water.
- Wind: Wind brings in its load of dirt and debris into your pool water. These include leaves, fine organic particle from nearby vegetations, etc.
- Insects and other animals: If you possess a pool, you must surely have seen dead insects’ bodies, mice and other small animals that have drowned in the water.
- Surface runoff & Rainwater: Rainwater and surface runoff bring microscopic algal spores into your pool water. Surface runoff also carries bacteria and other microorganisms.
- Bird droppings: Yes it`s true and unfortunately birds are not trained to poo in specific places. Bird droppings bring organic particles to your pool but also its load of microorganisms that can be dangerous to human health.
As can be seen, the sources of contaminations are various. If the pool water is left unfiltered, the water will quickly turn cloudy, with particles floating and remaining in suspension, debris settled at the bottom. In the long run the water will turn green and turbid. Stagnant water is an ideal medium for the proliferation of mosquitoes, algae, bacteria, viruses, and other dangerous microorganisms. However, for filtration to be effective, it shall be coupled to a balanced pool water pH (7.0 – 7.8) and chlorine level between 1.0 and 3.0 mg/l.
Taking care of your pool will keep you safe from various health hazards and the water will remain crystal clear.
Vacuuming your pool regularly is also very important. Heavy particles that settle at the bottom won`t overflow or get into your pump suction system. Settled particles also includes birds’ droppings and organic matter which when decomposed will go in suspension; so better get rid of them while they lay at the bottom.
Selecting the Right Pool Filtration System
As mentioned earlier, we shall stress on sand filters while other types of filters such as diatomaceous earth and cartridge filters are also used for pool water filtration. Emphasis shall be put on sand filters as they are widely used, affordable and are easy to maintain.
The design of a good filtration system shall depend on various factors. The most important one, is the time needed for one complete filtration cycle, i.e., the time required for the whole pool water volume to pass through the filter. However, according to guidelines from “L`Agence Regionale de Santé (A.R.S)” – French guidelines for public swimming pools; the duration for one complete filtration cycle will depend upon the type of pool.
Filtration cycle time:
- spa pool: twice the pool volume per hour
- Wading pool: minimum 30 minutes
- Swimming pool with water height equal to or less than 1.50 m: 1hr30 minutes
- Diving pool: 8hr
For domestic pools it is strongly advisable to have your pool water volume filtered in a maximum of 4 hours and have your pool pump programmed for 2 complete cycles per day.
Pool filter sizing (surface area & diameter):
We shall base our example on a 25 m3 domestic pool.
Recommended filtration velocity for pool water: 30 – 50 m/h (50 m/h usually used as basis by most pool filter manufacturers).
Maximum time for one complete cycle: 4 hours
Therefore, recycle volume per hour (flow rate) = 25/4 = 6.25 m3/h
Flow rate (m3/h) = Area (m2) x Velocity (m/h)
Therefore, for a 25m3 swimming pool, required area (A) = Flow rate/ Velocity = 6.25/50 = 0.125 m2.
Now, Area , where = 3.142 and r is the filter radius.
Filter radius r = square root (A/3.142) = 0.2 m
Therefore, required filter diameter = 0.2 x 2 = 0.4 m = 400 mm.
Note: the above example shows how you can calculate the required filter size by assuming that the flow rate from the pump is 6.25 m3/h. However, if the pump has a higher capacity (for example designed to complete one filtration cycle in 2 hours), the filter size also needs to be revised, as it is important not to exceed the filtration velocity of 50 m/h.
Filtration media:
The most widely use filtration media is silica sand. However, glass media and anthracite are very good alternatives.
The recommended media size for a good filtration is 0.4 – 0.8 mm, offering a filtration capacity of 20 – 40 microns.
Backwash:
After some time, the debris and dirt particles accumulate in the filter causing pressure build up at the inlet of the pool filter. It is important that you backwash your pool filter at regular intervals so as you keep your media in perfect working conditions and your pool clean. However, don`t forget to rinse the filter after each backwash.
Choosing the right pump:
In the above example, the pool volume was simply divided by the number of hours to get the flow rate. However, other factors shall be taken into consideration, these are:
- Difference in height of filter and swimming pool.
- Distance of filtration room from swimming pool (this should be as minimum as possible).
- Pressure losses.
If you are not familiar at reading pump charts, better you seek advice from your pump supplier or from a professional in water treatment.
Sources:
https://www.vigipiscine.com/blog/temps-filtration-piscine
https://www.mrpoolman.com.au/blogs/news/what-do-sand-filters-remove-from-water
