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September 8th 2021
By Mike Fowler - Pool and Spa Marketing
When closing pools, the goal is to make the spring opening as smooth as possible. When it comes to keeping the water clean and clear, the industry knows the pool filter is key. Water treatment products help keep pools clean, but even chemical manufacturers agree, if the filter is not working properly, these products cannot provide clean and clear water alone.
Keeping filters in tip-top shape will make pool openings much faster and easier for service professionals in the spring. To do so, it is important to get back to basics and review how sand, diatomaceous earth (DE), and cartridge filters work. More importantly, pool professionals need to remember how the pump feeds water into these filters. Understanding the relationship between the pump and filter gets to the heart of obtaining clean and clear water.
Like any filter, once it gets dirty, it needs to be cleaned to continue to operate properly. Filter pressure is one of the best ways to determine if the media is dirty and needs to be cleaned. The change in pressure differential (kilopascals [kPa]/pounds per square inch [psi]) can help a service professional determine if a filter is dirty or needs to be backwashed.
For this information to be most effective, it is helpful if technicians keep a log of the filter pressure for each pool. Many will do this when they open the pool and leave the information posted near the filter in the pump room and/or log the data into the customer’s maintenance profile. Or some will mark ‘Clean’ on a pressure gauge so they know where they started and when it raises a minimum 10 psi above the starting point.
In fact, one of the most important figures to note is the initial pressure on the gauge at the top of the filter tank because if a pool is having trouble with water turbidity or with the heater cycling while trying to maintain the proper water temperature, service techs can start their diagnosis by looking at the filter pressure reading. For instance, if the pressure reading during the pool opening was 124 kPa (18 psi) but now shows 207 kPa (30 psi) when the trouble is occurring, the first thing one should consider is a dirty filter.
To remedy this, service techs should begin by backwashing the filter to see if it fixes the problem. (Cartridge filters may require removing the media to clean). By restoring the water flow the filter will function properly, which should allow the water to clear—it might also fix the problems with the heater. As mentioned earlier, when the filter pressure goes up, the water flowrate goes down. Therefore, service techs who take the time to check the filter pressure when performing winterizing cleaning are taking the first important step toward ensuring smoother pool openings.
However, a newer challenge has presented itself now that variable-speed pumps (VSPs) have become extremely prevalent on today’s pools.
“In the past it was simple, the pump was either on or off, and you just took the filter pressure measurement,” says Dan Lenz, a manager at All Seasons Pools in Illinois. “However, now that the pump is not on at full flow all the time, it becomes harder to get an accurate pressure reading because as flow increases, pressure increases and not necessarily because of a dirty filter.”
As VSPs do not constantly operate at full speed, it makes it harder to obtain an accurate filter pressure reading. To overcome this issue, many service techs turn up the pump to the highest pre-set circulation speed (not the highest speed on the pump) and take a pressure reading during their weekly service.
Those techs who are not doing a weekly service should ask their customers to perform this task and tell them to call the pool service company if their filter pressure increases by more than 4.5 kg (10 lb). Running the pump at the highest pre-set circulation speed and checking filter pressure is part of the weekly service routine, along with cleaning the pump baskets, skimmers, etc.
Cleaning the filters when there is a large change in pressure is especially important with cartridge and DE filters as it can prolong the life of the filter. Following this procedure will also help to avoid compression and compaction of dirt and debris on the face of the DE grids and/or cartridges, making them last longer and easier to clean.
“In the past, it was common to keep an eye on the filter pressure reading. If there was an increase of 11.3 kg (25 lb), it was time to backwash or clean the filter,” says Lenz. “However, now with cartridge filters, cleaning the media when there is a 2.26-kg (5-lb) pressure increase is recommended. Sticking to this rule of thumb will help to prolong the life of the client’s filter. If a tech waits for a 4.5-kg (10-lb) change in pressure, the pleats will begin to collapse and the bands will start to break.”
Richard Deakin, a certified pool operator (CPO), certified pool instructor (CPI), and commercial product development manager at Hollandia Pool & Spa in London, Ont., says filter backwashing is very site specific, which poses several variables that need to be taken into consideration before backwashing, as well as determining the length of the backwash cycle.
“Industry standards state a sand media filter with single gauge should be backwashed when the pressure increases between eight and 10 psi from its starting setting. Dual gauge filters have an industry standard of a pressure differential of 10 to 20 psi,” he says. “That said, most operators backwash filters on routine, not on demand, which is counterintuitive to the functionality of these types of filters. My advice, however, is to get to know your system and its limitations, and work within those limits.”
Automatic controllers can be invaluable when it comes to knowing when to backwash a dirty filter. Rather than having a tech perform weekly manual checks, the automation system can be set to backwash the filter based on its pressure readings. Pool professionals who truly understand the filter/pump relationship can incorporate these best practices for cleaning into their winterizing routines and help their customers achieve clean and clear water in the spring.
The most common cleaning procedure for any type of pool filter is backwashing. That said, there are several best practices for each filter type. The following are some tips service technicians can use based on the type of filter they are working with.
Sand filters
Sand filters are still one of the top filtration methods used throughout the industry and, therefore, it is important service professionals are aware of the proper backwashing and sand cleansing procedures for this equipment.
Technicians should begin by determining the proper backwash flowrate 57 to 76 litres per minute (lpm) (15 to 20 gallons per minute [gpm]) per 0.1 m2 (1 sf). For example, a 0.28-m2 (3.1-sf) sand filter needs no less than 176 lpm (46.5 gpm) and no more than 235 lpm (62 gpm).
Too much water flow could potentially lift the sand bed and pass it to waste or worse, it can damage the laterals and/or filter tank from the sand blasting effect as the water is introduced at the bottom of the tank at a high velocity. However if there is not enough water flow, the debris will not be entirely removed from the sand bed. Anything that is left to remain will work its way deeper into the filter.
Should this occur, the debris at the bottom of the filter can turn to ‘caliche’ (a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt) and the equipment will likely need to be replaced as it is extremely difficult to remove because of its size and the inability to break it up.
“When we open up the filter to winterize the pool, we discover the laterals are broken or we see sand in the pool, which often means the laterals are broken,” says Brett Huston, the owner of Patio Pleasures in Wisconsin. “We keep extra filter parts on our trucks, such as laterals, O-rings, gaskets, and multi-port valves, so we can quickly and efficiently fix our customers’ filters.”
That said, it is good practice for service companies, as part of their winterizing procedures, to fix any problematic filters before the pool is closed. It is also suggested service techs warn the customer that there can be a lot of time and cost associated with changing the media in a sand filter. For instance, in extreme cases, a technician could spend a better part of a day chiselling out sand from a filter. Therefore, it is important technicians know how to keep a sand filter functioning properly. One of the best ways a service tech can do this is by adding a dry clarifier when cleaning the media. When a technician is performing this procedure it is important they first turn off the inlets for all chemical feeders. Then, with the pump running, and the filter in the backwash position, 170 to 453.5 g (6 to 16 oz) of dry clarifier should be added through the skimmer. To do this, the skimmer basket, along with any material in the skimmer, has to be removed first. Then, based on the pool’s volume, a technician should add 4.9 mL (1 tsp) into the skimmer for every 18,927 L (5000 gal) of water. After adding the clarifier, the filter should be operated normally.
The clarifier can also be added directly into the filter media and left to soak for four or more hours. After soaking, the pump should be started with the filter in the backwash position.
The clarifier completely washes out the filter during the backwash and does not leave any residual. As sand does not necessarily filter out small particles (small micron size), adding a dry clarifier can help the customer’s filter work better as it increases filter efficiency by penetrating the sand with a highly effective polymer formula to restore water quality after heavy bather loads and/or rain. The product attracts all matter as small as two microns and captures it in the filter.
Another problem with backwashing sand filters can occur when it is done too frequently in dry and/or dusty regions. In some cases, silt can pass right through the filter when it is clean. When this happens, service techs often get calls from customers saying they have sand in their pool and additional sand comes out of the pool returns when they are vacuuming. To diagnose this situation properly, technicians should start by brushing the pool to see whether the sand makes a pile or a cloud in the pool. If the former happens, there could be an issue with the filter; however, if the latter occurs, it is silt not sand.
If it is ‘silt,’ the problem is the sand filter is too clean and, therefore, it should not be backwashed. When a sand filter is very clean, it allows larger particulate to pass through. This is a sign for technicians/homeowners to stop backwashing the filter and, instead, allow it to load up so it can trap the silt. A clarifier or flocking agent can be added to the filter to help with this process.
Technicians should not determine how long to backwash a sand filter by looking at the water flowing out of the line. They should not guess, either. That said, it is a good idea for service pros to use a stopwatch when performing this task as it should not take any longer than three minutes.
It is also important to remember that eventually the sand in the filter must be changed. The media has a lifespan, too, and at some point it can no longer just be cleaned. That said, the job of changing the sand can be challenging and time consuming.
“Depending on the size of the filter and how dirty the sand is, changing the media can take us anywhere between one and six hours to complete,” says Huston. “In terms of how frequently the sand needs to be changed, it’s a good idea to set expectations with the customer. For example, when dealing with our commercial pool clients, we tell the facility operator they must change the sand every three to five years depending on the bather loads of the pool.”
Pool professionals use a variety of tools when cleaning and changing sand from filters. Generally, a shop vac is used to speed up the process, as opposed to doing it by hand; however, some technicians may resort to using screwdrivers, chisels, or whatever can fit into the narrow area available once the filter has been opened.
“We prefer to change the sand in filters in the spring—after it has sat empty all winter and has dried out—so the sand doesn’t have all the water in it making it heavy,” says Huston. “The lighter the sand, the easier it is to remove it quickly.”
Diatomaceous earth filters
Unlike sand filters, frequently backwashing DE filters does not affect the filtration rate. However, it does create extra work and expense for service techs. Similar to sand filters, DE media should be backwashed for three minutes; however, the procedure should be broken down into a one-minute backwash, followed by one minute of filtration for three separate cycles (the pump should be shut off each time the tech switches between modes). This procedure helps separate the DE coating from the grids, allowing it to be removed from the filter.
A DE filter should be backwashed at the same 69 kPa (10 psi) increase over normal operating pressure as any other filter media. These filters should be torn down, cleaned, and degreased by a service tech at least twice a year. Body lotions and sunscreen collect on the grid material, and simply backwashing the filter will not remove these films. That said, it is also recommended service techs use a degreasing agent to complete the filter maintenance process. Technicians should also note: muriatic acid will permanently lock the oils and lotions into the grid material and, therefore, it is not recommended.
When recharging the DE filter, one should always follow the manufacturer’s recommendation as to the amount that should be used to charge the filter. The proper way for a technician to do this is to use a 19-L (5-gal) bucket to mix the water and DE together to create a slurry. Then, the slurry should be poured slowly into the skimmer while the pump is running. This will ensure the grids or elements are properly coated from top to bottom.
Cartridge filters
Cartridge filters are not designed to withstand water flow in a reverse direction; therefore, it must be taken apart to clean. The process is completed in the same manner as a DE filter teardown—hosing the surface debris off the cartridge is the first step.
Body oils and lotions are the number one contributor to a plugged cartridge filter. The oily buildup on the surface plugs the pores on the cartridge, which restricts water flow. It also creates a very sticky surface. Therefore, getting this debris off the cartridge surface is the difference between frequent media replacement and those cartridges that last a long time between cleanings.
Cartridge filters trap dirt on the surface. When the filter is turned off, the debris falls to the bottom of the tank to free up more surface area for the next cycle. If the surface of the cartridge is sticky, the debris does not fall away. Instead, it can plug up the filter rather quickly.
Many pool professionals now offer winterizing cartridge filter cleaning services. When performing this service, technicians not only hose off the filter, but also soak it with muriatic acid and a filter cleaning agent, then re-soak it with a liquid chlorine bath to brighten and lighten the filter (making them look nicer when returned to the client). The filters should be allowed to air dry before they are used again.
“We like to remove cartridge filters when we close the pool because temperatures fluctuate throughout the winter and early spring, causing mould can develop in the media which is very hard to remove,” says Huston.
Joe Koch with Blue Wave Pools in New Jersey says his company performs an enzyme wash and acid dip on DE and cartridge filters.
“When we winterize a pool we perform a general cleaning of the filter. At this time we determine how dirty the filter is and whether or not the media can be cleaned with a hose-off alone,” says Koch. “If further cleaning is necessary, we take the filters back to the shop for deep cleaning.
Koch’s team starts by soaking the filters in an enzyme wash overnight to break down all of the organics on the filter. The next morning, they perform an ‘acid dip,’ which removes all of the minerals.
“This process makes the filter cartridge look like new every time,” says Koch. “This is a great money-making service that keeps our guys busy in the winter. After we clean the filters, we bring them back to the customer during the winter to re-install them. During this visit, we also take the opportunity to check on their pool and winter cover.
“This gives us an extra visit with our customer to talk about other opportunities for upgrades for the following spring,” says Koch. “It’s always good to remain in contact with customers over the course of the winter.
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