Welcome to our Ultimate Guide to Pool Filters! Filtration is an integral part of keeping your pool clean. Here we go over how filters work, the different filter types, and how to choose the right filter for you. We also included a bit of troubleshooting to keep your filter running strong. Let’s dive in!

How Pool Filters Work

Pool Filters all work similarly; the pool pump pushes water into the filtration unit, where it passes through a medium and is then returned to the pool. The filter media traps dirt, debris and algae. As more debris becomes trapped, the pressure of the filter increases, requiring the media to be cleaned.

While you might think the filter is for catching dirt in your pool, it’s primary function is actually capturing algae. Removing trace amounts of algae prevents it from being able to grow in your pool.

What’s Backwashing?

Backwashing is where the flow of the filter is reversed so that trapped debris can be sent to waste. This allows cleaning the filter without having to physically take it apart. Backwashing typically involves turning a valve or two while the pump is off. When the pump is turned back on, water is pushed in reverse and debris and some filter media then exits the system to waste.

Cartridge filters do not have the ability to be backwashed, since they utilize a cloth medium.

Types of Pool Filters

The big differentiating factor between pool filters is the type of filter media they utilize. The three types of pool filters are Sand, Cartridge, and Diatomaceous Earth (D.E.). Each one has their pros and cons.

Sand Pool Filters

Sand filters are the lowest cost and maintenance option for pool filtration. Sand filters utilize a bed of special sand that traps debris as water passes through it.

Sand Filter Diagram

Diagram of Cartridge Filter: water is pumped into the cavity, forced through the sand media into the inlets, and then recirculated to the pool.

Sand Filter Pros

  • Backwashing: Sand Pool Filters offer the lowest level of maintenance. Cleaning it requires a simple turn of the valve to backwash, then turning the valve again to filter. Super easy.
  • Cheap: Sand Filters are the most inexpensive type, ranging in price from $250 to $650. Sand is also by far the cheapest media to purchase. The average cost for Filtration sand is $0.25 / lb.

Sand Filter Cons

  • Lowest Filtration Ability: Standard sand can filter down to about 20 microns, making it the least effective in terms of what it can capture. There are special types of sand that can help it filter down further, some claiming to get close in efficacy to D.E. Filters.
  • Channeling: Sand filters sometimes develop what is called “channeling”; over time, water will create channels through the sand, greatly reducing the amount filtered out. This is fixed by breaking open the filter and using a garden hose to fill up the tank. This loosens the sand and allows the channels to break up. However, sometimes you’ll need to change out the sand completely depending on how bad clumping is present.

Cartridge Pool Filters

Cartridge filters are the middle of the road when it comes to filtration and price. Cartridge filters run between $450 and $850. They utilize a cartridge that contains cloth filter media that will trap as small as 10 microns. Since they don’t use a powder or granular media, the cartridge must be removed and cleaned when dirty. Cartridges themselves are expensive compared to Sand and D.E. powder, averaging around $50 each. However, cartridges last a long time, you only need to buy one (and not a bag full) and you don’t need to add anything to the filter for them to work.

Cartridge Filter Diagram

Diagram of Cartridge Filter: water is pumped into the filter cavity, forced through the cartridge, and then pushed back into the pool via the return line.

Cartridge Filter Pros

  • More Effective than Sand: Cartridge Filters are twice as effective as sand, filtering down to 10 microns.
  • Doesn’t Require Sand or Powder: The cartridge unit does all the work, and cartridges last a long time.

Cartridge Filter Cons

  • Can’t Backwash: Cleaning involves removing the cartridge unit itself and either spraying it off with a hose or soaking it.

D.E. Pool Filters

D.E. Filters are the top end of filtration. They are built a bit like cartridge filters, with a spiral grid pattern in the center. These grids are covered with Diatomaceous Earth powder, allowing the filter to capture debris as small as 5 microns – giving this type of filter the most efficacy.

D.E. Filter Diagram

Diagram of D.E. Filter: water is pumped into the filter chamber and forced into the grids through a layer of diatomaceous earth, before being sent back to the pool through the return line.

D.E. Filter Pros

  • Highest Filtration Ability: D.E. Pool Filters are the most effective – filtering down to as low as 5 microns. This makes them 4 times more effective than sand, and twice as effective as a cartridge.
  • Backwashing: Like sand filters, D.E. Filters can be backwashed. However, after backwashing D.E. more D.E. powder must be added to the skimmer to recoat the grids.

D.E. Filter Cons

  • Most Expensive: D.E. Filters are the most expensive to both purchase and maintain. D.E. Filters usually start at $850.00 and go up from there. D.E. Powder is about 4 times the cost of sand and must be added after every backwash.
  • Hardest to Break Down: D.E. Filters are harder to break down compared to Sand and Cartridge. There are more steps, and getting the grids to fit properly in their spiral pattern can be tricky.

Which is the Best Pool Filter for me?

Knowing the pros and cons of each filter, you probably have an idea with what you want to go with in terms of your filter type. However, if you’re still on the fence, this is what we’d recommend depending on what you want:

I Do My Own Pool, I Want Easy, and/or I’m on a Budget

Then probably Sand or Cartridge is best. They’re much easier to maintain, and a lot less expensive.

I Have My Pool Serviced and/or Want the Best

Then D.E. is the way to go. It offers the highest level of filtration, and the more thorough cleanings (a.k.a difficult) will be handled by your service professional. Just make sure to check and see what they charge for filter cleanings and whether it is based on the type of filter.

Troubleshooting Pool Filters

Filters are pretty robust, and when properly maintained usually don’t have too many issues. However, here are a couple problems that you may run into, and how to fix them.

It’s important to reference your owner’s manual for your filter when doing any maintenance. Always turn off the filter and bleed off pressure before disassembly and when turning the pump back on.

High Filter Pressure

High filter pressure indicates that the filter has become clogged or otherwise obstructed.

Sand

Perform backwash

Cartridge

Break down and clean

D.E.

Perform backwash

Filter not Filtering

If the filter is not catching debris and is instead shooting back into the pool through the return line, then it means the water is somehow bypassing the filter media. This will also cause cloudy water and lead to algae that seems persistent.

Sand

The sand is likely to have “channeling”. Break down the filter and using a garden hose with low flow, fill the sand tank until it’s overflowing. This will loosen the sand. You can also lightly stir and/or poke the sand to break it up further. If the clumping is severe, you’ll need to change out the sand. Be careful when pouring in new sand, since this could break the inlets at the bottom of the tank.

Cartridge

Either the cartridge is not seated properly, or the cartridge is torn. Remove the cartridge and look for any rips, holes or tears. If you find one, replace the cartridge. Also check any o-rings, pipes, etc. and replace as necessary. When you reassemble the filter, make sure everything is properly seated.

D.E.

There can be a couple reasons for this: the D.E. might not be distributed across the grids, one of the grids may not be seated correctly, or one of the grids themselves may be worn/damaged.

Break down the filter, and carefully remove the grids. Hose off all the old D.E. powder, and then check the grids themselves for any holes or tears. These commonly form at the edges and seems. Check inside the unit for any damaged o-rings and/or piping and replace as necessary. Put the filter back together, making sure all the grids are properly seated. With the pump running, add D.E. powder via the skimmer.

That’s It For Now!

Did we miss anything? Have a filter question? Let us know in the comments below!

Leave a Reply