Everything You Need to Know about Sand Filters

Sand filters are the first type of pool filters and are one of the best pool filters. As the name suggests, they are filled with sand, but don’t think you can just go to the beach and use that sand. It requires a specially graded sand to get particles 20 -100 microns so it will all debris and even most pathogens!

One of the nice things about sand filters is that they are very low maintenance. In fact, the dirtier they get the better it will filter since it is able to trap more. However, you don’t want it completely filthy (keep it under 10 pounds of pressure) because it won’t work if it is – but you’ll never really want it completely clean.

Sand Filters vs Other Filters

This section briefly goes over the differences between the various types of filters. This is not meant to be a detailed explanation, but will just offer a brief explanation and the pros of a sand cartridge over these others.

Sand filter vs DE Filter

Although DE filters are the most efficient and let the least things go through (they trap particles the size of 3-5 microns), they require a lot of work.

3 different pool filtersDE filters require a lot of internal assembly about once a year do be cleaned. In addition to that, cleaning them isn’t easy as a cartridge filter. They require hosings and chemical soaks can be very annoying and time consuming. However, at least this only needs to be done about 2-3 times a year.

While this isn’t a lot of work sand filters only need to be cleaned every few years making them very low maintenance in comparison.

 

Sand Filter vs Cartridge Filter

Cartridge filters don’t require too much work. They only need to be cleaned 1-3 hours, but when cleaning IS involved it usually requires hoses and chemical soaking. Cartridge pool filters also tend to leak pretty easily, giving you all the more reasons to consider classic sand filters.

Easy to maintain and with few breaking opportunities, sand filters offer some advantages for the pool owner who doesn’t want to spend his/her life just maintaining a pool.

Maintenance

The only thing you need to do to really maintain our sand filter is when your pressure gauge reaches 8-10 pounds of pressure. At this point it is better to backwash the dirt from the filter it or else it will soon stop working. Typically this happens every 1-2 months, but it varies a lot depending on your pool and environment.

We’ve mentioned the other filters require a lot more to work clean. Well, this is because the sand only needs to be replaced every 5-7 years. As the sand gets older it begins to not filter as well and will lose efficiency. However, it may be difficult to realize it since it is very gradual.

One of the easiest ways to tell if your sand needs replacing is how often you need to backwash it. If you find that you have to start cleaning it more and more often over time, then it is a good signal that the efficiency is going down and the sand should be replaced. Sometimes it’s hard taking off the cover so if you have trouble check out these top cordless drills.

Pool Filter Sand Problems

Mudballs

Sand Filter MudballOne of he biggest problems with pool filters is that the sand can clump up because of oil or the chemicals it filters from your pool. This phenomenon is called mudballing and the actual balls of sand are mudballs. The best way to get rid of this problem, by placing tennis balls in your pool to absorb the oil, will often work, but still doesn’t always entirely prevent these chunks of sand.

When this occurs the sand is not distributed well (it’s in a tight ball instead of being spread out)and water can go right through the filter. If you have hard water like we do in California then the high calcium water can cause a chemical change, modifying filter sand to sandstone and creating a very similar effect.

Improper Pool Equipment

Your pool system isn’t too fragile, but having the wrong equipment in it can create some annoyances. For example, having too weak of a pool pump will result in your water not being cleaned, but having too powerful of a pool pump will cause you to waste money on the pump and electricity. You can find a list of the best pool pumps here.

Oversized pool pumps also tend to cause sand deterioration within your swimming pool filter. This is because the water flows more freely throughout your pump, and it is actually siphoned into your pump faster and with more pressure. The powerful water that is being pulled in will wear down your sand more quickly and can result in more sand changes (3-4 years) instead of the typical 5-7.

Using Certain Pool Chemicals

Some chemicals such as biguanide chemicals (think of Soft Swim or Baquacil) can cause pool filter sand to create mud ball like problems. While the sand doesn’t come together into balls, it does tend to bunch up. Like with mudbals, it ruins the distribution and will allow some water to flow freely through.

To combat this the sand will need to be cleaned about once a year. However, if there are more oils and other chemicals in the pool the filter may require more maintenance.

Solving These issues

An easy way to to clean the sand (not replace) is to just add 300 mL of aluminum sulfate through the skimmer. This will help purify the water and reduce the amount of problems oily or hard water can create. However, D.E. powder is also effective in achieving similar results. Aluminum sulfate tends to work better though.

aluminum-sulfate

My favorite method to ensure maximum effectiveness is to replace the top couple of inches of sand with some filter sand substitute such as FilterGlass. It will improve the efficiency of your sand filter and make it less likely to be affected by oil and chemicals.

aluminum-sulfate

aluminum-sulfate

How to Backwash a Sand Filter

backwash visualizationWe’ve mentioned before that a good time to backwash your sand filter is when your pressure gauge reads roughly 8 to 10 pounds. This is an important process to understand and ignoring it will eventually leave your swimming pool filter useless.

The best part is that even though you have to do it every few months it is really easy. Basically, all you do is turn a handle and this will allow water to go through the filter in the opposite direction which is why its called back-washing. This process removes dirt from the filter.

However, if you see the pressure gauge signaling it is time for a backwash, don’t just turn the valve right away. Instead, you’ll want to shut down the filter pump or else you’ll create some fairly significant problems.

  1. Filter Mode – Your filter will always always be on “filter” mode, which makes sense considering that is not only what it is called, but also its main job.
  2. Recirculate – this doesn’t really see much use unless your filter is broken or leaking. While it won’t clean your pool at least it will keep the flow going, preventing damage and harm to your pool.
  3. Backwash Mode– this is exactly what you use if you want to backwash the filter and clean it out. Double check to ensure valves are open and backwash hose is not bunched up.
  4.  Rinse – This is only used after you have finished backwashing. It’s best to use this setting for 10 to 20 seconds.
  5. Waste/Drain – This setting will send the funneling water in out of the waste hose, effectively ‘throwing it away’, instead of allowing the water to return back to the pool. It’s good to use if you want to get rid of water to reduce the pool loevel such as if you want to use a pool vacuum to get rid of debris.
  6. Closed – This will prevent water from entering the filter. It’s best not to close out your filter while the pump is on since this can cause your pump to work excessively hard for no reason.

 

If you’re using the right equipment (filter and pumps) then you may only need to backwash about every 4-6 weeks depending on your pool and environment.

Filter Sand in the Pool?

A little sand in the pool never really hurt anyone. After all, it’s easy for wind to carry it in, or for swimmers to track it in with them as well. However, if you’ve noticed that your pool has been more sandy than usual, you may have filter sand in the pool.

The easiest way to tell if it is filter sand is if there is sand in a line that is directly in front of where the return ports are.

While there is nothing wrong with that, this may indicate a damaged filter such as a broken lateral. The primary issue of a sand filter is to have a damaged standpipe, which is a vertical pipe in the center of the filter. If it is cracked or completely broken then sand can easily escape from the filter and go back into the pool.

However, sometimes the problem is not directly with the standpipe, but with the laterals. Laterals are to standpipes as roots are to trees. They essentially are at the bottom of the standpipes and extend out.

Laterals are much smaller than the standpipe so they are more likely to get damaged during installation or later on – even though it’s not always obvious. If this is the case you’ll want to address the issue as soon as possible.

To fix it you want to open up the filter, remove all of the current sand, and find the cracked lateral/standpipe. From there you will want to replace it. If your filter is 6-8 years old then changing just the filter is sufficient. However, if it is older than that then you’ll want to think about getting an entirely new filter system/unit.

How Often Should I Replace My Filter Sand?

Most people tend to say you should replace your filter sand once every 6-8 years. This is what most commercial pool companies do, and it’s not bad guidance. However, if the filter is working fine, the pressure is under 24 PSI, and it seems like it’s not leaking then there isn’t any need to replace it.

You don’t want to change it if you don’t have to because older filter sand tends to work better than newer sand. This is because the debris will start to collect with the sand and help filter. While older sand is better, don’t try too hard to keep the sand just for this reason.

Older sand is very likely to develop channels (paths of sand) that allow water to travel through, thus not filtering the water. Also, sand becomes more oily as it gets older, but if you keep the chemical balance of the pool well then your sand can easily last much longer than the typical 6-8 years.

Filter Sand Replacement:

A lot of people want to know about filter sand replacement, and think that it’s okay to just grab any sand and put it in the filter. However, not all sand is created equal!

You’ll want to make sure whatever you buy has the words “pool filter sand replacement” or “pool filter sand”. If it doesn’t explicitly say so, then it is not meant for your filter.

What’s special about pool filter sand is that it is #20 silica sand and is .45-.55mm. It’s relatively easy to find filter sand at nearby Home Depots, gardening stores, or local pool stores. However, I have found it easiest to just buy it online. You can find the best pool filter sand here, by Aqua Quartz.aqua-quartz-sand

To replace, you will want first empty out all of the sand that is currently in the filter. To do so you’ll want to remove the drain plug and let the filter just start draining the water. Afterwards, on the top of the filter, you’ll find either the top dome or multiport valve which you will want to remove.

Start putting the sand in according to what the manufacturer recommends. It is normally about 2/3 to the top, but you’ll want to follow their suggestions very closely. You don’t want to fill it completely to allow some room. Then, put a little bit of water in to help the sand set. At this time, it may be a good idea to add a new o-ring while you’re at it.

Afterwards, (whether you’ve added the o-ring or not), put the top dome / multi port valve back on and double check to ensure it is on tight.

Replacing your Sand Pool Filter

Sand filters are one of the most important parts of your pool system if you want a clean pool. There are a couple of factors you’ll want to keep in mind. For example, you’ll want to make sure your filter is right for your pool size.

Don’t just skimp out on the cheapest one available, as they are typically the smallest which might be too small for your pool. If it is too small for your pool, you might as well not even have one. (not quite, but it’s really not very helpful).  Having an incorrectly sized filter may force you to spend more money later on so make sure to take the time to get the right sized one.

Sand filters are sold in different sized tanks which is based on diameter. Here, we’ve outlined a small guide for you to follow:

The first 2 numbers is the pool range and second set of numbers is the diameter range for the sand filter tank.

  • 10,000 – 19,999 gals – 21”- 24” tank 
  • 20,000 – 29,999 gals – 24”- 30” tank
  • 30,000 – 40,000 gals – 30”- 36” tank

 

While these are general guidelines if your pool has a lot of debris you may want to consider getting a bigger, more powerful filter. Unlike with other items, having a large filter for your pool is not bad and will still fit well into your system.

Conclusion:

Cheap and easy to maintain, sand filters are great options for sand filters. They are my personal favorite, and if you take great care of your pool then they can easily last well beyond the normal 5-7 years – up to even 15 or 20.

If you’re looking for a filter for your pool you’ll want to check out our review of some of the greatest pool filters.

Laurie S.

As a multi home owner for 15 years I've tried out a ton of pool products and methods and have found out the best ones that work for me. I love helping out other people with real, honest advice and spending time with my family. If you have any questions please don't hesitate to contact me in the about or through a comment.

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