When building your salt water pool – or when you have an existing pool and are looking for a replacement – you essentially have 3 types of pool filters to choose from:
- Sand filter
- Cartridge filter
- Diatomaceous Earth (D.E.) filter
What’s the best salt water filter for pools and how does each compare to one another? Let’s a take a look at each option and why you may consider one over the other.
Best Salt Water Filter For Pools
Salt Water Pool Sand Filter
This is the oldest style of filter and quite frankly I’d avoid using them at this point in time since there are better options. As the name suggests, the inside of the filter unit contains a special type of sand. When water passes through the unit, debris gets attached to the sand allowing clean water to get returned to the pool.
But over time as more debris gets caught in the sand, the pressure gauge will increase, water flow will decrease as will filtration efficiency and you must then clean the filter by backwashing it. This involves opening a valve and running dirty water out of the filter through a hose to rinse it. This of course means refilling the pool with water to replace the flushed water which over time increased your water and chemical costs. Water chemistry can be negatively affected as a result.
You also need to find out ahead of time if you live in an area where draining pool water into storm sewers is restricted and whether or not you are allowed to refill a pool with tap water. You may need to truck water in at your expense.
Sand Pool Filter Pros
- Typically the cheapest type of filter to use.
- Fairly low maintenance. Sand may not need to be replaced for around 5 years.
- Quick to install and easy to use in general terms.
Sand Pool Filter Cons
- Has the lowest ability to remove small particles of the three filter options.
- The oldest technology available for pool owners.
- Backwashing means having to replace water and chemicals more frequently which can negatively affect pool chemistry.
- Need to confirm that you are allowed to drain water into public sewers in your area.
Filtration level: Removes particles as small as 10-20 microns.
Sand lifespan: Sand typically gets replaced every 5-10 years.
Salt Water Pool Cartridge Filter
This is what our pool has and it’s the one I’m familiar with on a personal level. Our cartridge filter is a System 3 model from Sta-Rite. It’s a roundish black hard plastic pressurized unit that contains two round filter cartridges – the smaller cartridges sits inside the big one which is hollow in the center – with another small tube fastened in the middle with a small filter on the very top. So it’s effectively a 3 piece filter. These cartridges are also generally referred to as filter medium. So the filter is the unit itself and the filter mediums are the actual cartridges that sit inside, if that makes sense.
When water enters the filter unit, debris gets stuck on the pleats of the cartridges and clean water is returned to the pool. Over time, the filter cartridges gets full of debris and the filter needs to be taken apart and the cartridges rinsed as the picture above shows.
Cartridge Pool Filter Pros
- The best overall filter for both inground and above ground pools that will serve most pool owners well.
- Better filtration level than sand filters ie. can remove smaller particles.
- Relatively easy and quick to maintain. Rinsing filter mediums take 10-20 minutes typically.
Cartridge Pool Filter Cons
- Cartridges can be heavy to lift. The shipping weight of the 2 cartridges in our Sta-Rite System 3 is 75 lbs.
- Cartridges can be expensive to replace. There is a $350 replacement cost for our 2 cartridges.
- Algae causes problems for these cartridges and they have be thoroughly rinsed after bad algae breakouts, often more than once in my experience.
Filtration level: Removes particles as small as 5-10 microns. So it can remove particles half the size that sand filters can ie. it can filter smaller particles than a sand filter.
Filter medium replacement: Typically the cartridges need to replaced every 3-5 years.
I found that rinsing the cartridges doesn’t necessarily get them clean enough on its own. I found through trial and error that soaking the cartridges overnight in a large garbage bin full of water and a filter cleaning solution I bought at Wal-Mart definitely helped to further clean the pleats moreso than just rinsing with a hose. I did this once per season and it definitely helped to get rid of oils and other contaminants that I believe would not have been removed simply by rinsing.
NOTE: In my experience, algae wreaks havoc on cartridge filters. If you experience significant algae when opening your pool, once the algae problem is under control and the water is clear, you’ll want to rinse the cartridges. In fact you might want to rinse them while the algae problem is being sorted and then rinse them a second time when the problem is resolved.
Salt Water Pool D.E. Filter
The newest type of pool filter, it’s also the most expensive and time-consuming in terms of maintenance as it requires both rinsing the filter medium and backwashing.
D.E. Pool Filter Pros
- Provides the best filtration level of the three options able to filter particles as small as 2-5 microns.
- Offers the most thorough filtering of the three options.
- You may go several months without backwashing so it’s not as frequent as a sand filter.
D.E. Pool Filter Cons
- The most expensive and time-consuming filter to buy and maintain.
- Requires both rinsing the filter grids and backwashing the unit.
- New D.E. material needs to be added to the unit with every backwash.
- D.E. material used is recognized as a class 3 carcinogen by the International Agency for Research on Cancer so care needs to be taken when working around it.
Other Filter Components
It’s worth spending a few lines helping you understand related parts of the filtration system, namely the method by which water is delivered to the filter in the first place. Water passes through the filter by a pump which draws water from the pool usually from two places.
Typically, pools are built with two water intakes inside the pool as follows:
Main drain: Located at the deepest part of the pool at the very bottom, it draws water out of the pool through the pipes towards the pump to be refiltered and chlorinated before being returned to the pool through the return jets.
Skimmer: Located at the side of the pool in the deep end but usually around the middle of the pool lengthwise, it skims (as the name suggests) water off the top of the pool through an opening that like the Main Drain returns water through the pump for filtration and chlorination before the water is also returned to the pool. By skimming the top of the pool water, it draws leaves and other floating debris into a basket which you empty regularly to automatically keep the pool clean on the surface.
So you have two water intakes. One pulling from the bottom of the pool and one from the top. Typically you leave both valves open and allow water to enter from both sources simultaneously so that if one is blocked or constricted water flow continues from the other.
The main reason you shut one valve off – namely the main drain – is to concentrate all suction and water flow to the skimmer when you are vacuuming the pool. I can’t recall ever shutting the skimmer valve off but if it’s blocked, you can certainly do so to clear it.
- The best salt water filter for pools is one that properly filters water, requires relatively little maintenance and replacement parts and is easy to use.
- For the average pool owner, a decent cartridge filter will most likely serve its purpose without the increased water usage from a sand or D.E. filter that requires backwashing.
- Sand and D.E. filters also tend to require more maintenance time with backwashing which then means you have to refill the pool as water is drained and chemicals depleted.
- This is especially true if you live in an area where you are constrained by local regulations that limit or prohibit dumping large amounts of water in the sewage system or where filling a pool can’t be done through a garden hose legally.