In all swimming pools, there are only three types of filters. Most in-ground pool builders won’t give you an option. They will just tell you what you get with your pool and that’s it.
When buying an above ground swimming pool, there is usually an option on which filter system to get. Each of the three has its pros and cons.
D.E-type pool filters do the best job filtering but cost more and are more toxic. Sand-type filters are easiest to clean but don’t work as well as the two others. Cartridge-type filters work almost as well as a D.E. type, cost less, and are a simple design with fewer parts needing replacement. This is why I recommend cartridge filters.
WHAT IS A “MICRON RATING”? WHAT YOU NEED TO KNOW
I’m a pool guy, not a microbiologist. You are a swimming pool owner(or will be) looking to get the right filter. You don’t need to Google geek out on every little thing about how filters work. When choosing a type of filter, you might want to know this:
“A filter’s micron rating tells you the size of particle that can pass through it”.
As a general rule, the smaller the micron rating number, the better. This means that filters with smaller rating numbers will catch and filter smaller particles out of the pool water. That’s a good thing. Here are the micron ratings for all three filter types:
Sand filters 40 – 20 micron rating
Cartridge filters 20 – 5 micron rating
D.E. filters. 6 – 1 micron rating
As you can see here, the D.E type filter is the best because it takes smaller particles out of the water.
WHY MY OPINION IS A QUALIFIED ONE?
This is the internet. And if you didn’t already know, most information on the internet is inaccurate. When it comes to information and advice for above ground swimming pools, the information is gathered and written by people not in the real world industry. This really shows to a real pool guy like me.
For 37 years, I have been out in the Florida sun working on swimming pools. When I started my pool maintenance business in the late eighties, most pools had sand filters. The higher-end in-ground pools may have had a fancy D.E. type filter instead, and occasionally, I would see a cartridge type filter.
By the early 2000s, most of the existing sand filters were replaced by cartridge types and almost no brand new residential in-ground pools had a sand filter. This was in Central Florida and the other hotter areas of the country had the same trend going on.
In areas where it was hot, there was a long swim season, and where pools were more popular, cartridge type filters had now dominated the market. And they currently still do. Why? Let’s find out.
HOW DO THESE FILTERS WORK?
With all three types, the pool water has to travel through a medium. The medium catches or traps particles from the water, and then the water is carried back to the pool without the particles and is considered filtered. That’s about it.
1 How a sand filter works
Larger sand aggregate(bigger grains of sand) is poured into a tank body. The bottom of the tank body has a network of fine slits that attaches to a pipe that exits out of the tank. These fine slits only allow water to go through them (and not the sand).
As water from the pool enters the tank filled with sand, the water has to travel through the sand in order to make it to the slits at the bottom. As the water travels through the sand, particles in the water (some algae, dirt, oils, etc.) get trapped in the sand.
When the water makes it to the bottom of the tank, it enters through the slits (minus the trapped particles) and goes back to the pool as filtered water.
2 How a D.E. filter works
Plastic grids or fingers are suspended in a tank body and covered with a denim-type synthetic mesh material. This mesh material will only allow mostly water to flow through it.
The tank body is filled with water that is traveling under pressure into the tank and exiting out of the tank. D.E.(diatomaceous earth) (What is diatomaceous earth?) is introduced into the tank with the water so it can evenly coat itself to the grids or fingers inside. This is achieved as the water flows through the grids, leaving the DE powder behind by sticking on the grids.
With the grids in the tank now having an even coating of D.E powder in them, the water now has to travel through that thin layer of powder in order to get to the grids/fingers and travel out of the tank and back to the pool. As the water goes through the layer, particles(some algae, dirt, oils, etc.) get trapped in the DE powder only allowing the water to get back to the pool as filtered water.
3 How a cartridge filter works
A cylinder of pleated denim-type synthetic material is placed in a tank body. Water enters the tank body from the outside of the cylinder and then has to travel through the pleated material in order to get in the center of the cylinder where it exits out of the tank body.
As the water travels through the pleated material, particles(some algae, dirt, oils, etc.) get trapped in the material and water makes it back to the pool as filtered water.
THE GOOD, THE BAD, AND THE UGLY
All three types of pool filters can do the job well. But don’t think that one isn’t better for you than another. And this is the internet. You know, the place where we turn over every stone before we decide on something. Here then, is the pros and cons for all three filter types.
CARTRIDGE FILTERS (The Good) PROS AND CONS
1 PRO – Simple system – Out of the three filter types, the cartridge is the simplest. This is a good thing as it is easier to diagnose if there’s a problem and it won’t cost as much to repair.
2 PRO – Cost less – When comparing even quality levels, the cartridge filter is slightly less expensive than a sand filter and considerably less than a D.E type.
It’s very hard to tell the quality level of above ground pool filters, so don’t be fooled into thinking that one is a better deal than another. There are some good deals out there, but as a general rule, you get what you pay for with filters.
Cartridge filters cost less because they are simpler and don’t cost as much to make.
3 PRO – Less parts – Cartridge filters are designed with fewer parts than sand and D.E. filters. This is good because parts wear out and break. So, the fewer parts you have, the fewer parts there are to break and need replacing.
4 PRO – Works almost as good as a D.E. filter – I word it this way because there was a time when cartridge filters had a higher micron rating (see above). In the beginning, the micron rating for cartridge filters was only moderately lower(better) than sand filters.
Today’s (good quality) cartridge filters work just about as well as D.E. filters. I’m talking in terms of what a filter has to do in order to keep a swimming pool filtered. There are other filtering applications that really need much smaller particles captured. Pools have a range. And in that range, cartridge filters work very close to the same as the D.E. type.
5 PRO – Not a closed system – What I mean here is that, in order to do the regular cleaning for a cartridge filter, it has to be taken out. This is not like both the sand and D.E. type filter as they require backwashing for their regular cleaning.
Having to open up the cartridge filter to clean it is an advantage because you can see what is going on inside. You can see the condition of the filter element and know that it’s in good working order. With the other filter types, you cannot tell this because it’s closed when you backwash.
6 PRO – A new cartridge makes for almost a new filter – Good quality cartridge filter elements can last for years, but they will need replacing at some point. When they do though, the filter will work again as good as it did when it was brand new.
You can change the sand in a sand type filter(not necessary) and you can replace the grids in a D.E. type(very expensive), but they still may not filter like new. A new element for a cartridge filter will almost completely rejuvenate the filter. And it’s super easy to replace too.
7 PRO – It’s lightweight for winterizing up north – For areas that have extreme winters, it’s really nice to be able to store the pool’s equipment inside somewhere. With this, there’s no worry of the pump and filter getting damaged by the extreme snow, ice, or wind.
Cartridge filters can be disconnected, drained, and then carried to a basement or garage as part of the winterizing of a pool. Sand type filters don’t easily allow for this as they are too heavy.
8 PRO – Filter cleaning does NOT require pool water loss – Backwashing a filter requires some water loss from the pool. Cartridge filters don’t need backwashing.
9 CON – It takes longer and more effort to regular filter cleaning – Backwashing a filter is pretty easy. A cartridge type filter needs to be taken apart, and the element has to come out and get sprayed down to clean it.
Taking out the element and cleaning it with a pressure nozzle on a garden hose takes more time and effort than just backwashing.
10 CON – You have to buy a new cartridge – The cartridge or element in this type of filter will need to be replaced after a period of time. Most quality elements will last years before needing replacing, but they won’t last forever.
SAND FILTERS (THE BAD) PROS AND CONS
1 PRO – Cost less – In comparing equal quality, sand filters cost considerably less than D.E. type filters.
2 PRO – Regular filter cleaning is easy – Sand filters only require backwashing to clean them. This is the easiest cleaning method.
NOTE: Some will have a long backwash hose that will need to be run out into the yard with every backwash. This will make it harder and take longer to clean the filter.
3 CON – It’s a closed system – When backwashing, a sand type filter doesn’t need to be opened. This means that you will never know the true filtering status of the filter on the inside.
A sand filter can be partially clogged or “caked” up, and because you never need to open it, you will never know. This means that maybe only a portion of the sand is filtering inside instead of all of it.
The only way to know the real filtering status of a sand filter is to take the top off (usually the multi-port valve) and feel the inside with your hand and arm. This is a pain to do.
4 CON – It doesn’t filter as well – The micron rating for a sand filter is much higher (not as good as) than both the cartridge and D.E. type filters. This means it doesn’t filter as small-sized particles as the other two types.
With a good quality sand filter, a pool owner may not notice the difference during normal operation. But if the pool ever turns green, a sand filter will have a much harder time getting the water back to clear and clean.
This is not just based on the micron numbers. During the sixteen years of my having a pool maintenance business, I had to bring a lot of pools from green to clear. When green pools had sand type filters, they took a much longer time to get back to clear and clean.
5 CON – It has more parts – The more parts a thing has, the more that can go wrong. A sand filter has more parts than a cartridge type. Expect to have to replace parts of the multi-port valve at some point.
This can be even more problematic when it comes to filters made in China or made by some fly-by-night company that is here today and gone tomorrow. It can often be impossible to find parts, resulting in a pool owner having no choice but to buy a completely new filter.
6 CON – Old technology – The very first swimming pools didn’t have filters at all. They just constantly added new water and constantly had water exiting on the other side.
The first filters were mainly sand filters. This was from observing all natural bodies of water using sand as a filter at their bottoms and embankments. This old technology still exists and is a proper filter application for some things. But no longer for private swimming pools. And certainly not for above ground pools, which need as good of filtering as its smaller budget can provide.
7 CON – Requires pool water loss during filter cleaning – Backwashing requires water. This may not be a big deal during the rainy season or in more humid areas that don’t have a big rate of evaporation.
In areas where water is expensive or there is a lot of evaporation, the water used to backwash a sand filter is a consideration.
8 CON – Too heavy to move for winterizing – Sand filters are really heavy and bulky. It can really difficult to move.
In north areas where the winter is harsh, some above ground pool owners will want to bring their pool equipment into the basement or garage to prevent damage from the snow, ice, and wind. Sand filters make this a tough option.
Note: Some empty their sand filters every fall so they can move and store it. The next swim season, they add new sand or some other alternative.
DIATOMACEOUS EARTH FILTERS (THE UGLY) PROS AND CONS
1 PRO – Has the best micron rating – Anyone who knows about pools can argue that a D.E. filter is the best filter type in terms of filtering pool water.
A D.E. filter has the lowest micron rating, which means it takes the smallest particles out of the water.
2 PRO – Regular filter cleaning is easier – D.E. filters are backwashed as it’s regular cleaning. The old diatomaceous earth is backwashed out into the yard and new is easily introduced through the skimmer.
This isn’t quite as easy as backwashing a sand filter, but it’s pretty easy.
3 PRO – Lightweight for storing in the winter – As mentioned above, some pool owners who live in the north will elect to store their pool equipment indoors during the harsh winter. A D.E. type filter is lightweight enough to easily do this.
4 CON – Cost more – D.E. type filters clearly cost more to purchase than a sand or cartridge filter. This is, of course with comparing equal quality.
5 CON – Usually needs more repair than the other types – D.E. filters are a more complex system. It has more internal parts and is more susceptible to breakage.
During my many years of repairing filters, D.E. types break more by far than the other two types.
6 CON – It’s a closed system – D.E. filters are backwashed and then new diatomaceous earth is introduced through the skimmer to recoat the grids inside. This means you don’t have to open it up to clean it.
This also means that you don’t really know the status of the grids inside and therefore don’t know if they are dirty or clogged up. With this, the filter could just be working at half capacity and you wouldn’t know it.
7 CON – Will need to be taken apart for a deep cleaning – When I had my pool service business, we would take D.E. filters completely apart at least every 18 months for a deep cleaning. Some needed it more frequently than that.
Most D.E. filters don’t come apart easily as they are not designed to be opened very often. This can be a pain but is absolutely necessary if you want the filter to last and not have issues.
8 CON – Diatomaceous earth is very toxic – Other than its higher cost, this is my biggest “con” for DE filters. D.E. is a fluffy, white powder that appears harmless, but be assured that it isn’t.
I had been a pool guy for a few years before I found out about DE powder. At first, I thought it was as harmless as flour(which is what it looks like). Then during a routine backwashing, I got some of it in my eye. And it messed up my eye pretty bad.
I wondered how my eye could be in such bad shape with just a little white powder getting in it. When I got home that day, I did some (one-eyed) internet research on what diatomaceous earth really was and how toxic it really was. It turned out that that fluffy white stuff I was working with was bad news.
After my eye recovered, I never saw D.E. powder the same again and have taken precautions when handling it ever since. This is why, in this article, I’m calling D.E filters “the ugly”.
SAND, CARTRIDGE, OR D.E. FILTERS. WHICH ONE DO I RECOMMEND?
If you have read at least a portion of this article, you already know that I recommend a cartridge filter over the other two.
Cartridge filters are less expensive, work well, and don’t break as much. I have noticed that some people who live in the north will prefer a sand filter and there are those who want the best no matter what, so they think D.E is the way to go.
Pool owners in the north like sand filters mainly because that is all they know. The trend years ago that I spoke of earlier of sand filters being replaced by cartridge types occurred more in the southern states. In the north, it’s not as crucial to have a good filter as the swim season is not nearly as long.
Then there are the people who want the best no matter what, so they will opt for a D.E type. I get that as I too am one of those people. In truth though, the only real advantage that a DE filter has over a cartridge is when having to bring a green pool back to clear. With all things being equal, the DE will make the pool clear faster.
This is the only advantage a DE filter has though, so even though I want to best, I won’t go with a DE because when considering all things, it’s really not the best. A cartridge type is.
The proof of how I feel about this is that I have a cartridge type filter on my pool at home. And I wouldn’t have any other type, even if it was free. Which it has been.