Sand filters are a pretty standard feature in residential swimming pools. They are relatively simple to operate, and they use a natural media, sand, to filter the water of fine debris.
But, they have some pluses and minuses, so you should do some research before deciding if they are the right choice for you and your swimming pool. Let’s get started.
What Are Sand Filters And How Do They Work?
Sand filters start with a hollow tank on a stand, just like other filter types. Inside the tank, there is a pipe at the center, usually made out of PVC plastic. Very old sand filters might have a metal pipe, but that is pretty rare to see.
Diagram: A) Pressure gauge, B) Air relief valve, C) Air relief tube, D) Diffuser, E) Lateral assembly
The pipe extends from the diffuser neck at the top of the filter tank down to the bottom, entering a manifold or hub. The hub has a series of slotted pipes that branch out across the bottom of the tank like spokes on a bicycle wheel. There is a valve affixed to the top of the tank that allows you to control the flow of the water through the tank.
At the heart of this operation is, you guessed it, sand. The sand filters the water of fine debris, as it is packed inside the tank and around the internal plumbing. Typically the tank is filled about 60% of the way with sand, so the amount you need depends on the size of your filter tank. We’ll talk a bit more about what sand is best to use a bit later.
When the pump is activated, and the valve is in filter mode, it forces pressurized water into the tank from the top or side. The water is forced through the sand, cleaning it of fine debris, into the bottom of the tank, where it enters the slots on the manifold pipes. The water then collects in and rises through the center pipe. Finally, the clean water passes through the valve and back to the pool.
When you turn the valve to backwash mode, the movement of the water reverses, and the fine debris is flushed out of the sand and into an outlet pipe or hose that eliminates the dirty water from your system.
Pros And Cons Of Sand Filters
Sand filters have pros and cons associated with them. As a quick reference, these are some of the things you should know about before you buy one.
- Easy operation
- Relatively inexpensive filter media (sand)
- Common design familiar to most pool professionals
- Routine backwashing is required
- Discharged wastewater can be a hassle
- Water is lost each time you backwash
- Sand is very heavy, and replacing it is labor-intensive
- Access to the system for repairs can be difficult
Sand Filters vs. Cartridge Filters
Aside from the biggest and most apparent difference in filtering media, there are some other differences between filters with a cartridge or sand system. Cartridge filters don’t need backwashing. Instead, you have to open the tank and rinse the grids by hand. So, they do not usually have a multiport or a valve attached.
That can save you some money. Multiport valves can cost a few hundred dollars, and plumbing them into a system can be a little bit complicated, especially for a DIYer or a novice. Multiports also include a special gasket (called a spider gasket) that allows them to work. That gasket can be easily damaged, even during routine changes of the valve’s position.
The multiport itself usually has a sight-glass so that you can see the water discharged during a backwash. That’s important as the wastewater is often diverted into a buried pipe, so it doesn’t make a mess on your lawn. Without the sight-glass, you won’t know when to stop backwashing.
But, those sight glasses tend to leak a bit and get stuck easily.
Often constructed of real glass, they are exceedingly easy to break. And, without one in place, you can’t pressurize the lines with air to purge the water when closing your pool for the off-season.
Another difference between sand and cartridge filters is that sand filters work better when they are a little bit dirty. The dirt actually helps filter out finer debris than the sand can filter on its own. What happens is that the fine pieces of debris fill in the voids around the sand crystals, narrowing the gaps and filtering even finer debris.
The biggest downside of a sand filter compared to a cartridge filter is replacing the filter media. At some point, you will need to replace your sand. Changing out a cartridge is easy to do, and you can usually just wash a cartridge and reuse it. Changing out the sand means opening the top of your tank and scooping or vacuuming out all of the sand through a narrow opening. More on those specifics later.
A sand removal job is not an easy task, and when it’s complete, you still need to reload new sand into the tank and close it back up. This labor is a significant drawback, and many homeowners with larger sand filters end up hiring a pool professional to handle the task of changing the sand.
Sand Filters vs. DE Filters
Sand filters have a big advantage over DE filters, though they do operate on similar principles. You do not have to add sand to your filter after a backwash, as it all remains in the tank. When backwashing a DE filter, you actually rinse away the DE, along with the dirt caught in it. That means each time you backwash, you also have to add a new DE to the system.
Working with DE isn’t extremely dangerous. But, some people are very sensitive to exposure, and you might want to consider wearing gloves and safety goggles when handling it. It’s also not a good idea to inhale DE if you can avoid it, as the dust isn’t healthy for your lungs and can be an irritant or worse. You can always wear a mask to minimize any health risks.
But, since you’ll be working with DE quite often, you are probably going to get tired of using all the safety gear and resort to just holding your breath and squinting a bit to keep it out of your eyes.
Safety concerns aside, it is quite easy to make a mess with DE. If you add it to the skimmer’s mouth too quickly, some will fall to the bottom of your pool, and you’ll need to vacuum it out. And, even if you are pretty careful, you’ll probably end up spilling some on your deck.
One way to minimize spills is to buy small, single-use bags of DE instead of a big one that might last a whole season or longer. But, the smaller bags are a little bit more expensive.
DE also filters down to a much finer level of debris. While that is helpful in keeping your water clear and clean, it can also be a bit of a hassle when the pool is dirty, like when you first open it each season or after a heavy storm.
The DE will become inundated with debris quite quickly, and backwashing will be required quite often. Sometimes, that might mean multiple backwashes every day until the water clears up.
For more information comparing these types of filters, head over to my complete sand vs. DE vs. cartridge filter comparison.
Criteria You Should Consider When Looking For Sand Filters
When you’re considering a sand filter, you need to consider the size of your pool to make sure you have enough volume of sand to handle the amount of water you’ll be putting through it. If you don’t know how many gallons of water are in your pool, use our swimming pool volume calculator. The manufacturer’s recommendations and the total surface area of the sand will help you decide which size is right for your specific application.
Sand filters are probably the most common filter type on the market for swimming pools. Since they are very common, you should be able to get parts without too much difficulty when needed. But, if you’re going to be servicing the filter yourself, be prepared for some hard work any time you need to change the sand.
For more tips on how to find the right filter, head over to my best pool filter guide. There you’ll find a lot more detailed criteria on choosing the right filter and my top picks from popular brands like Hayward, Intex, and others.
Tips For Cleaning Your Sand Filter
Cleaning your sand filter should be done regularly. But, you don’t have to open the tank to access the sand. Instead, your system will have a feature called a multiport or a slide-valve that allows you to backwash the filter media, which is, in this case, sand.
The multiport design is usually installed on the side of the tank, with an inlet and outlet union made out of plastic. Other times, the multiport is actually on the top of the tank. A slide valve is a simpler design compared to a multiport. A slide valve only has two or perhaps three positions: filter, backwash, and sometimes closed. A multiport can have settings for filter, backwash, rinse, closed, waste, and more.
In terms of cleaning the sand, all the valves accomplish the same thing. You switch them to backwash to rinse the debris out of your sand, flushing the wastewater out of the system. If you’re having trouble with your multiport valve, check out my multiport valve troubleshooting guide to know what to do when it is leaking or having other issues.
How Often To Change The Sand in Your Filter (And When It’s Time)
You’ll have to change the sand in your filter every 3-5 years, depending on a few factors. The sharp edges of the sand are what helps to really grab debris, and after a few years of interacting with the rushing water in your filter, those edges become smooth and less efficient. So, it’s best to set a schedule and stick to it to avoid problems before they get started.
But there are also some signs that indicate it’s time to change the sand. Some of the things to be alert for include:
- The pool water remains cloudy even after running the filter as usual
- Sand accumulates under the return jets in your pool
- You need to increase filter run time to keep the water clear
- Algae seems to occur more than expected despite keeping up with your water treatments
Sand filters can also develop an issue with limescale. Limestone deposits act as sand magnets, and they end up creating clumps of sand that decrease the efficiency of your filter. Sometimes, if left unchecked, all of the sand in your filter can become compacted into a dense, brick-like substance.
This problem tends to occur when the filter is not used for a long period of time or isn’t routinely backwashed. There are chemical additives you can purchase that will help mitigate the risks of limescale.
What To Do With Old Pool Filter Sand
Old pool filter sand is actually a bit dangerous. Not only is it filled with the impurities it filtered out of your pool water, but it is potentially quite dangerous to inhale. So, don’t be tempted to use it for toys or litter boxes. It is also too fine to be used in concrete mixes.
But it can be stored safely in buckets and used for winter traction in icy conditions. Or, it is actually just about the right size and consistency for creating a base layer for a paving stone patio or walkway. It can also be used to fill holes in your lawn before adding topsoil. Some people just bury it to be safe.
Where to Find Sand For Your Sand Filter And What Kind to Buy
You can buy pool filter sand online, in a big box store, or from a pool chemical vendor. The best kind to buy is what the manufacturer of your filter recommends. Follow their instructions carefully, and let them dictate the type of sand and what quantity you use.
Some manufacturers suggest using a blend of sands with different coarseness at different layers within the filter tank. There are three primary types of pool filter sand:
- Zeolite – Highly porous
- Pool Filter Sand – #20-grade silica sand
- Filter Glass – Recycled crushed glass
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How To Install A Sand Filter
Installing a sand filter is pretty much just like installing any other filter. It is plumbed into the system just after the pump, with a pipe running from the top of the pump to the filter’s valve and inlet.
If you are handy with PVC pipes, the process is pretty simple. A good practice is to dry-fit each piece of the assembly before gluing anything in place. Make sure your tank is level and that you follow the manufacturer’s recommendation for adding sand and the size of pipe you are using for your plumbing.
An easy way to end with a big problem on your hands when working with PVC is to over-tighten it. It’s very easy to crack. So, a good rule of thumb is to get a threaded fitting only hand tight and then put a quarter-turn extra using more leverage or a wrench. This technique can help you avoid over-tightening and cracks.
Typically, the filter has a threaded union right at the attachment point for the valve. For added flexibility, if there is the opportunity to do so, you might want to consider installing a separate union between the pump and the filter itself and even on the lines to and from the pool.
This way, if you ever need to take something apart to access the system, you don’t have to cut any pipes. You just unscrew a union or two.
Now, set your valve to backwash mode and turn on your pump to rinse your new sand to flush out any impurities. Never change the position of your valve with the pump running. Shut your pump off, switch the valve to filter mode, and enjoy your pool!
If you want even more info on sand pool filters, check out these guides too:
- Swimming pool sand filter problems and how to fix them
- How to replace laterals in a sand filter
- Sand in your pool? How to get it out
- Why is my pool filter blowing out sand?
- Sand filter calculator
As always, don’t hesitate to drop me a line if you have any questions.