Spa & Hot Tub
Filter Information

The spa filter is one of the most abused and unappreciated part of most spas. Water is being forced through it every second your spa is being run and it's cleaning your water of algae, leaves, bacteria, hair, oils, dead skin, bugs, dissolved solids, and any other debris and gunk that gets into the water.

There are three different types of filters available, each of which has its own unique advantages.

Diatomaceous Earth Filters are made of grids of extremely fine mesh that are coated with diatomaceous earth. The DE acts as an adhesive, trapping any small or microscopic dirt particles in the water. DE is made from crushed petrified bones that, if you were to look at under a microscope, would look like a sponge with thousands of tiny pores. One of the advantages of DE is that it's organic and non-polluting. In other words, it's environmentally inert. Do note, however, that some municipalities or other environmental authorities have strict regulations regarding the disposal of DE. This becomes a concern when it's time to clean the filter by backwashing it.

Sand Filters use sand as a filter medium. Inside a sand filter is a certain amount of sand and gravel, which mix with water passing through, pulling out dirt and impurities. Small microscopic particles can escape capture in a sand filter. To prevent this, you can use a product such as Spa Bright and Clear to coagulate the particles into larger particles the filter can catch before the water is sent back into the spa. Every few years, you may also need to add new sand to the filter. But do note: These filters require a very specific type of sand.

Cartridge Filters are the most common filters is spas and this page refers to them.The cartridge's are made with a fine, pleated mesh material (usually dacron). The pleats are the key to the filter's operation. The tight pleats, or folds, allow for a large amount of material to be used in a small container. The more material used, the larger the surface area available to capture unwanted dirt or debris in the water.

Since the life of a filter is a tough and important one, it's best to prepare your filter by following a few simple maintenance rules;

Make sure that the spa runs for at least one hour each day to ensure good water circulation and turnover of the spa water (even if no one is using the spa that day). This provides sufficient filtering time for most spas. Also make sure you add Spa Bright and Clear (water clarifier) to the spa once per week, as this assists in filtering. ( not use a water clarifier if you're using PH Balance).

How often your filter cartridge needs replacing is dependant on a number of factors; the size of the filter, how often it's cleaned, how much the spa is used and how much debris gets into the water. Generally a filter needs to be replaced every one or two years, or if you notice any of the following; either of the plastic ends are cracked, fabric pleats separating from the plastic ends or cleaning it doesn't appear to get it any cleaner.

How often the filter needs to be cleaned also depends on the size of the filter, how much the spa is used and how much debris gets into the water. Generally portable or self contained spas should have their filters cleaned once a month. The best way to clean them is to blast them with a hose fitted with a high pressure nosel (some people clean their filters at a local self serve car wash). Don't use any cleaning products not especially designed for cleaning filter cartridges. If your fitter is very dirty, it can be soaked over night using "Leisure Time Spa Cartridge Clean".

Make sure to use some type of floating oil absorbing sponge (like our " floating duck") in your spa, as these will greatly reduce the amount of oils that get into your filter. Remember also clean and replace them when they deteriorate.

Do not use any soap based cleaners on your spa or the filter, and don't use car wax on your spa. Cleaners designed for spas, like "Spa Gloss " work the best.

Make sure you maintain proper water chemistry at all times. Filters are good, but they're not miracle workers and cannot actually kill off algae or bacteria ! Use a reliable test kit.

It's not a bad idea to have two filters and use them on an alternating basis.Switching them so that they may be cleaned thoroughly without loosing the use of your spa.

Try to shower before using your spa. The worst enemies of filters are,  hair spray, mousse or styling gel, deodorant or anti-perspirant, sun tan lotion, excess sweat and skin creams of any sort.

Conclusively, it's most important to keep oils or soaps of any kind out of your spa ! Remember, a spa is not a bath !

Following these simple handy suggestions will greatly add to the clarity of your spa water, and keep your filter working for months and months !

Filter Cartridge Cleaning Instructions
(reprinted from Unicel's® instructions)

When should a cartridge element be cleaned?

For swimming pools, clean the cartridge when filter canister pressure reaches 8 PSI above the initial system or new cartridge starting pressure. For spas, established a routine cartridge-cleaning schedule based on the amount of spa usage. If baquacil is used as a sanitizer, the filter element must be cleaned with Baqua Clean before any cleaner is used (step 4). Please refer to "cartridge cleaning supplement for baquacil users".

What is the procedure to clean my cartridge?

  1. Remove the cartridge from the filter housing following the manufacturer's instructions.
  2. Use a garden hose with a straight flow nozzle to wash down the filter element. Work from the bottom down, holding the nozzle at a 45-degree angle, and wash all the pleats with emphasis between pleats.
  3. Rinse until all dirt and debris is gone.
  4. For all spa cartridges and elements used in swimming pools where perspiration, suntan lotions, and other oils are present, soak the element for at least one hour (over night is most effective) in (1) a filter cleaner; or (2) one cup tri-sodium phosphate (tsp.) to five gallons of water.
  5. Rinse the cartridge again to remove oils and cleaning solution.
  6. If the filter has a coating of algae, calcium carbonate (residue form the calcium hypochlorite), iron, or other minerals, soak the cartridge in a solution of one part muriatic acid to twenty parts water until all bubbling stops. WARNING: failure to remove all oils and cleaning solution before acid soaking will result in a permanent restriction of water flow and cause premature cartridge failure.
  7. Rinse the cartridge clean and reassemble housing.

Note: Unicel does not recommend the use of diatomaceous earth (DE) with cartridge filters. DE particles will become trapped in the body of the media and shorten cartridge life. If desired, a cellulose fiber (synthetic DE) can be used in moderation.

What should I know about cleaning my cartridge element if I use Baqucil?

Unlike chlorine, which oxidizes the bacteria in the water, the active ingredient in Baquacil- polyhexamethylene biqunaide (PHMB)- destroys the bacterial cells. PHMB locates and binds to the bacterial surfaces, and then attacks the outer bacterial wall. Once this wall has been compromised, the inner cell membrane (the cytoplasmic membrane) is destroyed. This destruction allows the cell contents to disperse into their surroundings where they are further broken down into their elemental parts by Baqua Shock, a non-chlorine oxidizer.

In addition, Baquacil is a mild coagulant, which combines bacterial cells and other small particles in the environment into particles large enough to be trapped by the filter. The resulting deposit is a gray sticky film on the media, which can only be removed with Baqua Clean. If trisodium phosphate (TSP) or any TSP type cleaner is used prior to stripping the film, the cleaner and the gray film will combine to form a gum-like substance. Once this occurs, the substance cannot be removed from the media and the filter cartridge must be replaced.

WARNING: follow all manufacturers' instructions, warnings and cautions when using Baquacil, Baqua Shocks, and Baqua Clean.

Unicel Brand Filters FAQ

When should a cartridge filter be acid washed?
Is there an easy way to know when to clean a cartridge filter?
End Caps - Some cartridge end caps are hard and others are soft. Some cartridges have one hard end cap and one soft end cap. Why is this?
What does the term "plumbed backwards" mean and how can you tell if your system is plumbed backwards?
I saw a new filter cartridge made with yellowish material. What is this and why are Unicel cartridges white?
How can I tell when a cartridge filter element needs to be replaced?
Sharp pleat folds vs. rounded pleats — is there a difference?
Support bands — why are they put on some cartridges and not others? / What if the band breaks or comes off?
What is the procedure to clean my cartridge (chlorine and bromine spas)?
Is there a glossary of filter terms?


Caution:  Due to the possibility of high pressure build up in the filter system, it is important to take steps to alleviate this pressure before attempting to service the filter. Always shut off the pump, and open the air-relief valve or pump lid before removing the filter clamp and opening the filter.





Short duration's between necessary cleanings

Improper cleaning

Wash the cartridges thoroughly and carefully. As needed, remove the cartridge and soak in a cartridge cleaning solution to first remove any oils. If the cartridge is white and crusty and indicates calcification, mix 1 part muriatic acid into 3 parts water in a plastic bucket. Always add acid to water. Soak the cartridges until the foaming stops and the calcium deposits are gone. Thoroughly rinse the elements and reassemble the filter. Make certain that the valves are positioned properly, the pressure gauge is working, and the plumbing has no obstructions.

Water not balanced

A reliable test kit is imparitive. High pH or total alkalinity levels cause calcification of the filter element. Low sanitizer  level encourage algae growth, which clogs the pores of the cartridges. Be certain that the pH, total alkalinity and hardness levels are kept within the recommended ranges.

Improperly sized filter system

The filter may be too small for volume of water needed to be treated. Increase the filter size, if necessary.

Over-sized pump

An over-sized pump will cause dirt to penetrate the space between the fibers of the cartridges and cause shorter filter cycles. The flow rate should not exceed 1 gpm per square foot of filter area.

The filter does not appear to be cleaning properly. i.e. the water is cloudy

System is not running long enough or is incorrectly sized

Try increasing the time the water is filtered each day. On some systems with small filters, as they get clogged they filter less and less water.

Water not balanced

A high pH and or total alkalinity can cause calcium deposits and cloudy water. Low chlorine levels encourage algae growth and give a cloudy, green-or rust-colored tint to the water. Adjust the total alkalinity, pH and chlorine levels.Superchlorination if there is noticeable algae. Use a water clarifier (Spa Bright and Clear) to help remove particles to small for the filter to trap.

There is air in the filter tank

Air will prevent water from passing through portions of the filter elements. Bleed the air from the filter Check for leaks on the suction side of the system, and/or check the water level in the spa.

Cartridge not properly seated, is torn, or has become weakened

Be sure that the cartridge is properly seated and that there are no tears between any of the pleats. In addition, cartridges can become weak or "mushy" over a period of time and may allow water to pass over the top without passing through the filter. If this is the case, replace the cartridge element.

Water is leaking around the filter area.

Damaged/worn o-rings, tank, or loosened plumbing fittings

Determine the origin of the leak. Turn the pump on and bleed by opening the air-relief valve. If the filter is leaking at the clamp, remove the clamp and filter top, and clean and inspect the entire area and o-ring. The o-ring should be pliable and round, or needs to be replaced. Also inspect the mating surfaces of the top and bottom portions of the filter assembly for cracks. If the tank itself is leaking remove and repair or replace. To reassemble, lubricate the o- ring with a silicone or teflon based lubricant, and tighten the clamp or locknut securely.

If you need an exploded view / parts list & diagram of a particular filter, below are links to various pictures we have here so far. If the filter you're looking isn't listed, feel free to Contact Us and we'll put it up here for you(if we have or can get it). If you need a specific part, let us know.

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