There seems to be a lot of confusion about pool filters nowadays, especially when there is so much choice available. Fact is that a pool can be properly maintained with any of the filter systems available: Sand, Cartridge or Diatomaceous Earth (DE), and each has its own merits and demerits. The section criteria usually are location & use of pool, water availability and filtration quality standards. Below is a brief description of each type of filter:
Sand – The bullet proof filter
In a sand filter, the water is pushed through a bed of filter sand and removed through a set of lateral tubes at the bottom. The filter area of a sand filter is equal to the area of the filter itself. For example, a 24″ filter will have 3.14 sqft of filter area. Only the top 1″ of sand is actually used to filter the water. The principle behind this filter is that water is pushed through the filter sand, somewhat like an espresso machine. Dirty water goes in the top and clean water exits out the bottom. As the filter sand becomes plugged with debris from the pool, the pressure increases on the filter and the water flow drops. In order to clean the filter, you just run it in reverse and dump the waste water; this is referred to as “backwashing” the filter. Once the filter is backwashed, you move to the rinse mode and that repacks the sand and then back to filter. This has to be done manually every few weeks. From a hydraulics standpoint, a backwash valve is typically the most inefficient piece of equipment you can add to a swimming pool system. Should the sand ever become really dirty, it is easily and inexpensively replaced. In terms of particle size filtered out, sand is the lease effective method – it can allow smaller particles to pass back into the pool.
Cartridge – The economic low maintenance filter
This one is easy to understand. Water passes though a filter material and the filter captures the debris. This is just like the water filters used under your sink. Cartridges have much more available area to filter than sand. Most start at 100 sqft and some large cartridge filters sold are larger than 300 sqft. So they don’t clog up as quickly and therefore you service themless frequently. There are two types of cartridge filters in general. In the first case, there are filters elements that are inexpensive to replace and as such, they don’t tend to last as long. Then there are other filters that have very expensive elements and these last 5 or more years. In both cases, cartridge filters are designed to run at lower pressure than sand. This puts less back-pressure on the pump and hence you get more flow and turnover for an equivalent pump size. Generally these filters have to be cleaned once or twice a season by simply hosing them off, so you don’t touch them as often. In terms of particle size filtered out, cartridge is somewhere between sand and DE.
DE – The water polisher
Diatomaceous Earth is mined and is the fossilized exoskeletons of tiny diatoms. They are used to coat “grids” in the filter housing and act as tiny sieves to remove debris. They are very small and as such can filter out particles as small as 5 microns. Diatom filter area are sized between sand and cartridge – around 60-70 sqft are most common. Once the filter pressure rises, the filter is backwashed just like a sand filter and then “recharged” with more DE powder. Typically it is poured in a slurry into the skimmer and it then coats the filter grids. DE filters run at higher pressures than cartridge filters and as such can lead to some inefficiency and flow loss.
Best Filter?
Now with that background information absorbed, which filter is best? And the correct answer to this question is, ‘Can you please define best?’
If you want bulletproof robustness- sand is a good choice.
Low maintenance would lead one to cartridge.
DE would give you the cleanest water.
The fact is that all filters work and you can add a little DE to a sand or cartridge filter to increases its ability to filter small particles. Alternatively, flocculants can be added to the pool water to create big particles out of small particles.
Our recommendations would be to go with a high-end cartridge filter. The reason is that no one really wants to have another item on the to-do list and good cartridge filter can last a season. Keep in mind that the more square feet of cartridge, the less often you need to service it.
Remember, cartridges that become fouled can be replaced easily and cheaply.
If you need help with choosing your filter, please give us a call on 07950972561 or fill out the form on the right and we will call you back.