There are three basic types of pool filters, all in widespread use - Sand, DE (diatomaceous earth) and Cartridge. Each type has its pros and cons, but when used properly, any of the three will do an excellent job of keeping your pool clear and free of all but the smallest particles.
Before we get into the details of the individual types, let's spend a minute looking at what they have in common. All three filter types are used in series with your main pool pump, allowing the water to pass through the filter media before re-entering the pool. The media traps dust, dirt, oils, hair, and other small particles and removes them from water column. As a general rule of thumb, it is a good idea to oversize your filter. A larger filter will ensure you have adequate surface area and will also allow you longer periods of time between cleaning.
First we'll look at Sand Filters. Sand is by far the easiest to maintain but its filtering ability is the lowest - down to about 30 microns. This can be particularly evident if your pool is lighted at night. Filter aids such as DE powder or cellulose fiber, however, can help improve sand's filtering ability. Cleaning a sand filter is easy - when the pressure reaches a certain level (see owners manual) simply backwash the filter to remove the trapped dirt and debris. Back-washing is about a 10 minute process. The constant back-washing will tend to throw your water balance off but this can be useful if you use trichlor or cal hypo. Sand does occasionally need a more thorough cleaning than back-washing alone can do. Perhaps once a year, I recommend opening up the filter, sticking a garden hose in the sand and turning it on. Let the water flush out all the crud that has collected in the sand until the overflow is clean. You might have to CAREFULLY break up the sand with something like a broom handle if it is clumped together! (I said CAREFULLY so you don't damage the laterals!) If there is evidence of scale buildup then an acidic sand cleaner might be in order!
The next, and most effective filter media, is DE (diatomaceous earth). DE is made up of fossilized diatoms (porous, sponge like microscopic organism) and can filter down into the 3-5 micron range! If you do a lot of night swimming in a lighted pool you might want to invest in one since this is where the difference in water clarity really can show up. DE, however, requires a little more care than sand. There are 2 basic kinds of DE filters, the bump and the backwash. The theory behind the bump type is that when the filter gets dirty you 'bump' the dirty DE off the grids so it can mix with the dirt and then re-coat the grids with dirty DE! (I must confess I never quite understood the logic behind that--dirty DE is dirty DE!) The other type is the backwash type and while it can be back-washed, it really NEEDS to be broken down on a regular basis. In fact I will go as far as to say that back-washing them is not a good idea at all. When you backwash you never really know how much DE you remove so you never really know how much to put back in. The first time you have to break down a DE filter and chip away the hardened DE powder from between the grids of an overcharged filter you will understand what I mean! Also, back-washing forces dirty water BACKWARDS through the grids. We are always cautioned about running a DE filter without DE in it so we don't foul the grids but isn't that what we are doing every time we backwash one? Once again, this is a good case for soaking the grids once or twice a year. Be aware that some townships require a DE separation tank for back-washing DE filters. This can add to both the expense and the space they take up on your equipment pad.
Finally we have Cartridge filters. You either love them or hate them....there seems to be no middle ground here. Personally, I love them. There is no back-washing so your water balance tends to stay put (a plus with a SWG, a minus if you use trichlor!). Their filtering ability approaches DE in particle size filtered out (as low as 10 microns.) Cartridges do wear out and need to be replaced every few years. For very big pools they are not practical since you will be stuck with one of those 4 cartridge monsters that are a real pain to clean! However, some townships have outlawed sand and DE filters so in those areas, cartridges are the only choice. Proper cleaning is not hard but it can be a bit messy. Wear your swimsuit so if you get a bit wet it's no big deal. Cleaning is about a half hour process. You have to remove the lid, pull out the cartridges and wash them individually between the pleats, using a pressure tip water hose.
Remember, any filter type you choose is going be a compromise between filtering ability, ease of maintenance, and real estate taken up on your equipment pad. Just research your options and make a decision on what you think will fit best into your lifestyle. I don't think you will regret your decision no matter which filter you choose!
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