"Of all the places in my house, I love my kitchen best" is an old saying. "Of all the areas about a pool, I love the pool filter best" is my favorite saying. I do love a perfectly working filter. Next to keeping your pool's chemicals balanced, your filter is the most important part of your system. It traps contaminants and cleans the water. The pool filter is one of the areas I check during my pool inspections for my customers.
So how do we go about choosing the filter? Do we go on price? On size? The one that filters the best? All of these do play a factor in our decision making process. First, let's understand what a pool filter is, then we'll dive into the options.
What Is A Pool Filter?
The purpose of a pool filter system is to keep your pool water clean and clear. It's a very simple process. Dirty water is passed through the filter, the dirt and contaminants are trapped inside the filter media, and then clean and clear water is returned back to the pool via the returns.
Your pool filter acts exactly like all other filters on Earth. Your air conditioner filter, oil filter for your car, and lint screen/trap on your dryer are all the same. The dirty "whatever" flows in, the contaminants get trapped, and then the clean "whatever" comes out the other side. That's all a filter does, but it's an immensely important piece of equipment.
Types Of Pool Filters
So now we understand the main function of a pool filter. Now let's dive deeper and learn what our option are. The three types of pool filters we can choose are sand, cartridge, and D.E. filter.
Pool filters are gauged and measured by how well they clean and remove debris by microns. What's a micron, you might ask? It's "a unit of length equal to one millionth of a meter". To put it in layman's terms, it's really small. For a comparison, a human hair is about 50 microns, while a white blood cell is about 25 microns. Yeah, that's pretty small.
Sand filters are the most common type of pool filter, and for good reasons. They're less expensive, easy to operate, and filter fairly well. If you're a budget minded person and want spend minimal time on maintenance, a sand filter might be a good choice.
Sand filters normally use #20 silica sand, Zeolite, or crushed glass for its pool filter media. Go HERE to learn more about pool filter media alternatives. The pool water enters the filter tank through the top port, the water is pressed down through the filter media, and then clean water exits the filter and is returned back to your pool. Most, if not all, of the bacteria and contaminants are contained within the first few inches of the top of the sand.
Sand filters are able to filter down to 20 microns, which is smaller than a white blood cell. Just like D.E. filters, they have a multiport valve and do require backwashing when the pressure gauge is 8 - 10 psi higher than the "just backwashed" pressure. You can also increase your sand filter's efficiency by adding some D.E. powder in the skimmer.
It's recommended that you inspect your sand every few years and change the sand when needed. This is normally every 5 - 7 years, although some might not need to be changed for 10 - 12 years or longer.
Sand Filter Pros:
Easy to work on and easy maintenance.
Lower upfront cost.
Sand is very inexpensive.
Decent filtration efficiency.
Sand can last for years before needing to be changed.
Sand Filter Cons:
Least effective filtration compared to the other 2 types of pool filters. Can filter down to 20-microns.
Requires backwashing and rinsing which means water use can be upward of 250 - 300 gallons.
Broken lateral or standpipe inside the filter tank may cause sand to reenter the pool.
Do you want something better than a sand filter, but not as expensive as a D.E. filter? Do you require good filtration and something that's not too expensive to replace? Cartridge filters are very effective at capturing small particles, bacteria, and algae spores. Inside your filter tank is a plastic cylinder with pleated polyester with a plastic cap on each end. For reasons not known to me, I've seen more cartridge filters here in Florida than I did while I had my pool route in Arizona and the 11 years I lived in Oregon.
The pool water flows into the tank, through the pleats, and the debris, as small as 10 microns, is captured in the filter. The clean water is then returned back to the pool. Pool cartridge filters are inexpensive, easy to clean, and easy to replace. They normally last about 2500 - 3500 operational filter hours. I've personally found that cartridge pool filters are the best "all-round" in terms of a swimming pool filter system. They're easy for the first time and well-seasoned pool owner.
Cartridge Filter Pros:
Easy to clean.
Conserves water. No backwashing like a sand or D.E. filter.
Less parts inside the filter housing means less worry for you. When the cartridge filter is used up, throw it away and replace it.
Filters down to 10 microns.
Excellent choice for variable speed pump motors.
Cartridge Filter Cons:
Unlike simple backwashing, you'll need to remove the cartridge filter and manually clean it.
Cartridge filters only last a maximum of 3 years, or about 3500 filter hours.
Due to not backwashing and topping off with new water, your CYA can increase faster compared to a sand or D.E. filter that do require backwashing.
Not a good option for larger pools which would need several cartridges.
The most expensive type of pool filter to install and own also filters the best, and that's a D.E. filter. Diatomaceous Earth (D.E.) pool filtration uses diatoms, or diatomaceous earth, to do the filtering. Diatomaceous earth is the skeletal remains of single-celled organisms, and has the consistency of regular flour.
D.E. filters are the best type of filtration for your pool due to their incredible ability to filter and capture contaminants down to 5 - 7 microns. Inside the filter are either grids or, mostly for above ground pools, fingers-like appendages. You add the correct amount of D.E. to the skimmer to coat the grids or fingers. It's this coating of the grids that makes D.E. filters so effective at capturing the smallest of particles.
Just like sand filters, D.E. filters require backwashing and rinsing, which translates into water loss of about 200 - 300 gallons on average. For a heavily used pool, this certainly means a higher water bill as you will need to top off your pool each time you backwash.
IMPORTANT: D.E. is a known carcinogen, so care must be taken when adding D.E. to your pool skimmer. It's recommended to wear protective gear, including a respirator, when handling D.E. powder. Also remember, D.E. comes in 2 flavors: pool grade and food grade. We want to use pool grade D.E. for our pools, so be sure to carefully check the label to ensure you're getting the correct type of D.E.
D.E. Filter Pros:
Filters contaminants down to 5 - 7 microns.
Gives you extremely clear water.
D.E. Filter Cons:
Higher upfront cost compared to sand and cartridge filters.
Backwashing and rinsing requires using 200 - 300 gallons of water.
Pool filter size matters. Your pool pump and filter work together to give you perfectly clean and safe water. Pool pump motors and filters are both rated for GPM, or gallons per minute. This is the measurement of how quickly water is passed through the filter. The pump motor and filter should have the same GPM rating.
A faster, or a larger pump motor, is not always better. Huge calculations go into sizing your pump motor and filter. It is good practice to perhaps have a slightly larger filter, but the same logic doesn't translate well into a pump motor. Installing a larger pump motor can damage your equipment and decrease the effectiveness of your pool filter.
To keep it simple, you need at least 1 square foot of filter area for every 10,000 gallons of pool water.
What's The Best Pool Filter?
The pool filter you choose depends on factors such as ease of use, filtration capacity, and maintenance. If money is tight and you still want decent filtration, then a sand filter is the way to go. If you'd like a middle of the road filter that's not difficult to clean, then a cartridge filter is your best friend. If you want to toss a dime in the deep end and see if it's heads or tails, then a D.E. filter would be the one for you.
Regardless of the type of pool filter you choose, remember to maintain your pool chemistry, test twice per week, and add chemicals when needed.