How to Clean a Pool Cartridge Filter System

In this comprehensive DIY we're going to go over how to clean a pool cartridge filter. This How-To will work for virtually any pleated cartridge pool filter on the market. It will also work for jacuzzis and hot tubs with the same type of filter. We will go over which is the best and cheapest off-the-shelf product for filter cleaning. Keep reading to find out how to keep your pool in the best working condition without having to spend a fortune on new filters! Also, this guide might get updates over time. To see the latest version, click here.

Difficulty: Easy
Tool Requirements: Basic
Time: Between an afternoon and a weekend
Cost: <20$

Step 1: What You'll Need

Which Filters is this for?

This DIY was done using a Hayward C3030 SwimClear Cartridge Pool Filter (click here for the Owner's Manual) with it's four cartridge pool filters made out of pleated reinforced polyester. In any case, you can still follow the guide regardless of what brand you have. Simply skip over the model-specific details. The products and general process will be virtually the same for almost any other cartridge pool filter on the market. Nonetheless, It will best reflect the following Hayward SwimClear cartridge pool filter models:

What You'll Need - Main Items

Most of this you might have already, but probably not all of it. Here's a list of the items and tools I used.

Trisodium Phosphate (TSP) powder - This is the most important product. Before specific cleaners for everything became a thing, TSP was a staple for general purpose home cleaning. Just take a look at the ingredients of a few "Heavy-Duty" cleaners and you're sure to find TSP or a TSP substitute. It's still widely use for cleaning prior to painting since it is very strong, cheap, non-foaming and easy to rinse away with water. With regards to cartridge pools filters, TSP has been the go-to product for years - Unicel (one of the largest cartridge filter manufacturers) even officially endorses the method here. In my case (four large cartridge filters), I used 4.5 lbs to wash the cartridges twice. One benefit of TSP over normal soaps is that it won't create never-ending soapsuds, which would be undesirable here. As an alternative dishwasher detergent can also be used in a pinch.
Muriatic Acid - Also known as Hydrochloric Acid. It's a typical household and pool maintenance product. Muriatic acid will help clean the filter of algae, iron, calcium carbonate (residue from calcium hypochlorite), or other minerals. You will need approximately 1 to 2 gallons if you're cleaning your filters in a large trash can.
Plastic Trash Can - Depending on the number and size of the filters you'll be cleaning, you might be good with a 5 gallon bucket, or you may need a 50 Gal. trash can. You probably already have one already. In my case I used a 45 Gal. plastic trash can which was perfect for the job. Make sure you take note of the can's size since you'll be using it to make the calculations later.
Multi-Function Hose Spray Nozzle - Preferably multi-function and one that doesn't require keeping a lever held down continuously. I found the "Flat" setting to work best on this nozzle.
Silicone Paste- Unless you want to spend upwards of 50$ to replace all the rubber seals and gaskets (which will invariably be deteriorated if you use chlorine), the best option to help recondition, lubricate and seal the o-rings will be some silicon paste. Just make sure to use a paste like the one linked, which has a peanut-butter like consistency. That rather than silicone grease which is a lot more "runny" - more like honey. If you don't have this stuff already, you'll definitely find it useful around the house for any plumbing, water-related or automotive project.

Tools & Supplies

Rubber Mallet - To remove the filter's housing retaining ring in case it's stuck.
Rags and/or Paper Towels - For general cleaning.
3/8" Drive Ratchet- To loosen the housing's retainer ring.
3/8" Drive Torque Wrench- Since the owner's manual gives the spec for torque, I'd recommend the use of a torque wrench to properly get the right amount of pressure for a leak-free result. It's also the type of tool that, if you don't have one already, you'll find plenty of use for around the house and car.
19mm or 3/4" Socket- For the retaining ring bolt. You may need a different size if your filter is from a different brand.
Nitrile Gloves- Especially important for handling the muriatic acid. You should also find some safety glasses.
Measuring Cup - You'll need to dose some slightly nasty chemicals, so your significant other might not appreciate you using the kitchen's measuring cup. Your call.

What about "Commercial" pool filter cleaning products

Honestly, many of them will be little more than TSP and unnecessary additives or fillers. Or they just use acids. Unless the manufacturer of your filter mandates a specific product (and most likely even if they do), TSP should be the most versatile, cheapest solution. After all, a manufacturer can't really claim to have a "premium and durable reusable filter" if it were susceptible to such a diluted cleaning product.

What about "Pool Filter Cartridge Spray Cleaner Tools"?

If you've done your homework, you've probably seen Pool Filter Cartridge Spray Cleaner Tools made specifically for, well you guessed it, cleaning cartridge pool filters. If you already have one, by all means, use it. But if not, I don't see these worth the additional expense. It's just another hose attachment to damage or lose.

Your typical multi-function hose nozzle will do just as well and will serve for many more purposes. Just make sure it has multiple water patterns. I used this "Thumb-Control" spray nozzle which I found perfect for the job, especially because of the variety of patterns and not having to keep the trigger continuously held while washing the filters.

Step 2: When Should I Clean My Filter?

When it comes to deciding how frequently you have to clean your filter, thankfully you don't have to guess. Take a look at your cartridge filter's gauge - it will objectively tell you. In the case of this filter, it should be cleaned when the pressure increases by 8 to 10 PSI over the pressure initially measured with a clean filter. Normally your gauge should even have two arrows telling you when it's time to clean (as long as it was properly configured when installed). In my case, it took almost 2 years to need cleaning (though I recognize that may be the exception rather than the rule). I purposely over-sized the pool filter precisely to allow for longer intervals.

If your cartridge filter is undersized or your environment very dirty, I'd recommend installing pool skimmer socks or hosing down the cartridges (without chemical cleaning) every few weeks or months, as needed.

Also, to help lengthen intervals, I'd recommend periodically opening the drain valve on the bottom of the cartridge housing and then closing the pump output to flush any debris inside the housing out. That way you avoid silt or other gunk accumulating at the bottom. It would be best to do this at least once a month.

Step 3: Open Up the Filter Housing

Finally. Let's begin!

The first step would be to turn off the pump (especially important if it runs on an automatic timer) and close all the inlet and outlet valves, if possible.

Then, use a socket and a ratchet to remove the bolt holding the clamp together. You'll need a 19mm or 3/4" socket. Once it is removed you may need a rubber mallet to loosen the clamp if it's stuck on. Once it is off, the top housing can be removed, revealing the filters. Water will fall out when the top is removed. To avoid a vacuum being created, open the breather valve at the top (the orange lever). Or drain the filter housing altogether first.

Remove the Top Manifold and then the Filters. To help remove the filter cartridge elements apply a slight rocking motion while lifting up.

In my case, the Air Relief Filter Screen was falling apart and needed replacement. For any of these Hayward SwimClear filters the screen is the same part, regardless of the size. If your filter is also at least two years old you might want to order the part in advance to make sure it arrives prior to reassembly, to minimize downtime. To check if Ebay has it cheaper, click here.

Step 4: Flush the Filters With Water

As quickly as possible after removing them from the water, rinse the filters off. Use moderate pressure from a regular garden hose (no pressure washers!) and maintain at least a 45 degree angle to avoid damaging the filter. Place emphasis in flushing the debris out from between the pleats. You can also carefully brush the pleated surface to remove small particles and debris.

You will remove a great deal of crud from the filters, probably more than you would have imagined (picture attached for illustrative purposes). The filters were actually substantially lighter after cleaning, ironically enough. Choose the spot where you intend to clean the filter well to minimize clean-up later. I'd recommend on grass. It's just decomposed leaves, silt and fiber, so it isn't toxic. Just annoying.

Step 5: Submerge in TSP Solution

Now is the most important step.

You want to fill a bucket (or trash can, in this case) with water, and use approximately 1 cup of TSP per 5 gallons of water. I used roughly 2 pounds worth. Submerge the filters completely, and leave overnight if possible (3 hours minimum). Regarding using TSP substitutes instead of TSP, some users report lukewarm results compared to using the real thing. Given how sporadically filters are cleaned, I'd try to find the real stuff.

One cup dishwasher detergent to five gallons of water can also be used, but be aware that dishwasher detergent (for machine washing) isn't the same thing as dishwashing detergent (for hand washing). Dishwasher detergent is designed to not foam as much, and many are mainly TSP substitutes.

Afterwards, rinse off the filters to remove any loosened debris.

Step 6: Rinse and Clean the Filter Housing

While the filters are taking their TSP bath, I took advantage of the wait to clean the filter housing.

Clean the inside and flush any accumulated dirt at the bottom out through the drain. I then poured a cup of TSP here too, to really clean the inside. I also cleaned the outside of the housing and the bearing surface of the clamp to minimize work later on.

Finally, I reassembled the housing and filled it to the brim with water to let the degreaser act. I used a bamboo rod to make sure it was well mixed and dissolved. After a few hours I drained the fluid out and sealed it up. That way I could simply let the pump circulate (with no filters) to keep the water chlorinated.

Step 7: Submerge in TSP Solution - for the Second Time

Since it had been so long since the filters were cleaned, I gave them a second TSP bath. Everything is the same as before.

Step 8: Give the Filters a Muriatic Acid Wash

Should the filter have a coating of algae, calcium carbonate (residue from calcium hypochlorite), iron, or other minerals, a muriatic acid bath will help clean it. Personally, I think that if you've made it this far, you might as well do it even if the filter looks clean for good measure. However, make sure all oils and cleaning solution are removed before soaking the filters in acid as it might otherwise permanently damage filter. Though if you cleaned the filter as thoroughly as illustrated here there is little to worry about.

You will want to use 1 part Muriatic Acid per 20 parts water. Regarding the ratio, some recommend as much as 1:1, or as little a 1:29. In this case, I simply used one gallon of acid with as little water as needed to completely cover the filters - I estimate some 25 gallons. Remember to use gloves and safety glasses, as well as rinse any surfaces where acid may have splashed. If any acid falls on you, well, at least you can just take a leap in the pool.

Leave the filters in the bath overnight, or at least until the filters stop bubbling (if bubbling is present). Once you take them off immediately rinse them off in abundant water. To dispose of the bath, you can neutralize it with baking soda or ammonia, or dilute it was much as possible and pour it over your wet driveway or any safe location.

Step 9: Hose the Filters Down for the Last Time

You're almost done! Give the filters their last wash. Virtually no dirt should be coming out of the pleats at this point.

Step 10: Reinstall the Filters

Finally, we are ready to reinstall the filters. Pop them into the housing temporarily to keep them wet. Make sure the bottom seal plate is in the proper position prior to installation of the filters.

Step 11: Clean and Lubricate the Seals

Before reassembling, check the condition of the seals. In my case, they were deteriorated but usable. I cleaned them well and applied silicone paste (paste, not grease) to help recondition them as well as aide in sealing. I definitely like this paste in particular because of how thick it is, making it perfect for plumbing jobs.

The manufacturer cautions against applying lubricants, but then again they also say that the product should only be serviced by a qualified pool professional (I imagine cleaning would be included in that). Though they advise against its use, that would contradict the fact that they sell their own equivalent product stating that it is "Used on all metal parts or gaskets exposed to water, salt, pool chemicals or constant water pressure". I personally used it to avoid both leaks or having to replace an expensive gasket.

Clean all the O-ring grooves, lubricate the seals if desired, and put them in their place.

If your seals are not salvageable, or keep leaking after assembly, for this line of filters the replacements are Hayward DEX2422Z2 Metal Reinforced Filter Seal Replacement and DEX2400Z5 Outlet Elbow O-ring Replacement. If for whatever reason you lose or damage the nut and bolt, the replacement is DEX2421J2. For any other part numbers check the manual linked in Step 1.

Step 12: Reassemble the Housing

Now let's reassemble the housing.

Reinstall the clamp, lubricate the bolt threads if desired, and tighten the bolt. Hayward lists the torque spec at 150 inches-lbs, which is less torque than you would have expected. I'd recommend using a torque wrench as seen above, just to be objective.

Step 13: Clean and Refill the Pool

While the filter housing reassembly is completely done, I'd recommend cleaning the pool of major debris before starting up the pump. That way we'll have the most accurate measurement of initial pressure in the filter housing. Also remember to clean the skimmer baskets if applicable.

Also, make sure to refill the pool to the proper level if necessary. Here I'm using a Pool Sentry to fill the pool. It will automatically shut off the water once the pool reaches the right level, which is great if you're prone to forget that you were filling the pool.

Step 14: Take a Pressure Measurement

Now would be the time to take a pressure measurement. Turn on the pump and make sure you've purged all the air from inside the filter housing. You'll know you've properly purged the system when a steady stream of water (not air or, air and water mix) is discharged from the manual air relief valve. Also make sure you select the highest pump speed if your pump has variable speeds.

In this case the pressure dropped from almost 20 PSI back to under 10 PSI, which corroborates a job well done. Take note of this pressure so you'll know when it's time to clean the filter again (when the pressure increases by 8-10 PSI).

Note: When should I replace my filters?

When these filters were first installed, the pressure was around 10 PSI. After cleaning, the pressure went from 18 PSI back down to 10 PSI. The filters should be replaced (and not simply cleaned) when the pressure after cleaning is around the initial pressure plus 6 PSI. That means that if I were to have measured 16 PSI after cleaning (instead of 10 PSI), it would be time to replace the filters at the next cleaning interval.

Also, take note that the higher the PSI, the higher the opposition of the filters to the flow of the pump. In other words, the higher the pressure, the less water volume your pump is going to be able to move because it has to work harder.

Step 15: Enjoy!

Finally! The ordeal is over! You can be proud of having tackled the job instead of postponing it for a few months more. Hopefully this will buy some goodwill with your better half, too. You know you earned it.

Anyway, thanks for reading and I hope it was helpful. If you have any tips, tricks, questions or feedback, feel free to leave it in the comments below. Also, if you want to see more content like this, consider following me (there's a button at the top) or checkout out what other projects I've been up to. Here are a few you might like: