Different Types of Filters; Pros and Cons
Pool Filter Basics
There are really only three basic types of pool filters, and all are in widespread use. They are sand, DE (diatomaceous earth) and cartridge. Just like most things, each type has its pros and cons. When used properly, any of the three will do an excellent job of keeping your pool clear and free of all but the smallest of particles.
Let’s spend a minute looking at what they all have in common, and then we will get into the particulars of each individual type. All three types of filters are used in conjunction with your main pool pump, and allow the water to pass through the filter media before returning to the pool. The media in each particular filter works to trap dust, dirt, oils, hair, and other small items in the water. It is generally recommended to oversize your filter to the largest size possible, as it will do a better job of cleaning the water and require more time between cleanings. A larger filter will ensure you have adequate surface area to capture most everything that you do not want in your water! Bigger is definitely better in this area of your pool equipment.
Let’s start by looking at sand filters first. Sand is by far the easiest to maintain, but its filtering ability is the lowest of the three options, and only filters down to about 30 microns. This can be most obvious if you enjoy a pool lighted at night. DE powder or cellulose fiber can help improve sand’s filtering ability, if you choose this type of media and would like to see less particulate under lighted conditions. The sharp edges of the sand granules trap the dirt between themselves, which is what creates the cleaning process. However, as the water flows over the sand these edges get smoothed and rounded off and the filtering ability becomes lessened over time. New sand in sand filters is always better than old sand, and you will see a diminished ability to filter over time. Cleaning a sand filter is relatively simple; when the pressure reaches a certain level (always make a note of the clean filter pressure, and refer to your owners manual for any precautions and suggestions for cleaning) you will need to back-wash the filter to remove the trapped items. Back-washing is simple; about a 10 minute process. Constant back-washing has a tendency to throw your water off balance, but this can be useful if you are using tri-chlor or cal hypo as your sanitizer. Understand that sand does occasionally need a more thorough cleaning than back-washing alone can do, so do not think that you will never need to open the filter up or never look inside! Opening up the filter, sticking a garden hose in the sand and turning it on is helpful, and may be needed once a year or so, depending on your conditions and usage. Use the water to flush out whatever has accumulated in the sand until the overflow is clean. On occasion, you may need to break up the sand with something like a broom handle if it is clumped together or packed tightly. Be extremely careful if you need to do this so you don’t damage the laterals inside the filter. You may notice a bit of a calcium build up when the filter is opened, and an acidic sand cleaner may be helpful in this case.
Arguably, the most effective filter media is DE (diatomaceous earth). Diatomaceous earth consists of fossilized remains of diatoms, a type of hard-shelled algae, and is said to filter down into the 3-5 micron range. Going back to the example of lighting your swimming pool at night, you might want to consider DE, since this is where the difference in water clarity really becomes obvious. DE is not difficult to work with, but it does require a little more care than sand. Basically there are two (2) kinds of DE filters; the “bump” and the type that you back-wash. The bump type works on the premise that when the filter gets dirty you ‘bump’ the dirty DE off the grids, where it mixes with the dirt and then re-coats the grids. with dirty DE. This baffles many folks, since dirty DE is still dirty DE! The back-wash type can be back-washed, and while back-washing does clean it to some degree, it really does need to be broken down on a somewhat regular basis (usually once a year, or every six months in high usage/high filtering need areas). When you backwash a DE filter, you never really know how much DE you remove. This can be somewhat of a problem, as the DE material is the filtering media (It is needed to coat the grids inside the filter, as the grids are really too porous to capture much on their own.) and needs to be replenished to filter properly. If you add too much DE while guessing how much you lost during the back-wash, you will understand the first time you have to break down a DE filter and chip away the hardened DE powder from between the grids of an overcharged filter why this is not the best way to clean these filters! Back-washing forces dirty water backwards through the grids, just as the name implies. It is never a good idea to run a DE filter without any DE in it, as it has a tendency to foul the grids. Back-washing a DE filter is, in essence, doing just that, as the water is forced in the opposite direction of the normal flow, and runs the risk of fouling. This alone makes a good case for opening the filter once or twice a year, cleaning the grids, and replacing the old DE with new (the rule of thumb for DE replacement is one (1) pound of DE for every ten (10) square feet of filter area). Some areas require a separation tank for back-washing DE filters, which requires additional space on an equipment pad, as well as additional expense to obtain and install.
The last type of filter is the cartridge filter. In the industry, these are filters that are either loved or loathed, and everyone has their reason for their feelings. The biggest benefit is that there is no back-washing of cartridge filters, so your water balance tends to stay more consistent. A cartridge filter has the ability to approach DE in particulate size filtered out, and can get as low as 10 microns, depending on the manufacturer. Cartridge filters do wear out, but with proper care, they can last for many years. Some folks like to purchase a second set of cartridges and rotate them between cleanings (recommended cleaning of cartridge filters is when the psi changes to 10 pounds greater than when they were clean). Some cities have outlawed sand and DE filters, making cartridge filters the only choice. Cleaning a cartridge filter, like the other filter types, is not hard but it can be a bit messy. Expect to get wet as you spray off the individual filters (most cartridge filters have between one (1) and four (4) individual “elements” in them). Cleaning requires about a half an hour, and you need to remove the lid and pull out the cartridges; washing them them individually between the pleats. Use a high pressure nozzle on the end of your hose and spray the dirt of from the top down, doing both the inside and the outside of the cartridge. Cartridge filters, by way of their greater surface area (up to 520 square feet, compared to the typical 60 square foot DE filter, for example) hold much more dirt than the other filters, and can go longer between cleanings.
Like most things in life, no one filter is right for everyone. Water clarity, ease of cleaning, amount of available area in your equipment location and city restrictions all come in to play when deciding which filter is right for you. Research your options and consider which benefits of each type best suit you and your situation. In the end, they all do a good job, and one is right for you!
How to Maintain and Clean Your Pool Filter
Most people know that a filter is a key component of a swimming pool’s filtration system, but quite a few do not realize that the filter needs to be cleaned periodically. This is to insure proper equipment performance and cleanliness of the swimming pool water. This area will discuss why maintenance cleaning is a good idea, and then advise how to clean each of the 3 types of filters; cartridge (or cart), sand, and both types of the Diatomaceous Earth (DE) filters.
When your filter was brand new, the water could easily pass through it. The pounds of pressure per square inch (psi) that showed on the filter’s pressure gauge probably read about 8-20 psi, depending on your pool and its plumbing set up. However, as the filter does its job and filters, and the debris in the water gets removed, there is less room for more new debris to be deposited and the pressure rises. When the pressure eventually rises too much (usually by 8-10 psi over its clean pressure), it is time to clean out the stuff that has already been captured in the filter and make room to catch any new debris that enters the pool. Should you fail to keep the pressure in the normal range, you may experience cloudy water, poor circulation and excessive wear on the pool equipment.
In order to clean a cartridge filter, the pump must first be turned off, and any valves that would allow water to exit the pool must be closed. Next, open the drain port on the bottom of the filter and allow the water to empty, and then open the body of the filter. This may involve unscrewing some knobs, removing a nut at the top, or removing a bracket, which will allow you to then remove the cartridge or cartridges. You will want to make sure you note their position and orientation so that you have no trouble reassembling the unit when you have everything clean. Start by rinsing out the filter tank, and then take the cartridges to where you want to clean them. All you need to accomplish this is a garden hose with a nozzle on the end. Wash the cartridges from the top to the bottom, aiming downward at about a 45 degree angle. Remember to wash both the outside portion and the inner portion of each cartridge. It’s a good idea to start at an identifying point on the cartridge and wash all the way around. Repeat on the outside once the inside is done (or vice versa). When you are finished cleaning the cartridge(s), reassemble the filter and open any valves you might have closed. You are them good to go until the pressure raises by 10 psi, signaling time to clean again. If the pressure after cleaning does not return to your standard starting pressure, you may need to do a more through cleaning, or it may be time to think about replacing the cartridges.
Sand filters use a multiple position valve (sometimes called multi-port or multi) for cleaning the debris trapped by the sand medium. Please be advised that whenever you change the position on a multi-port valve, you MUST have the pump off or you will break something. Before starting, first make sure that any valve on the discharge line of the filter is open, and any discharge hose is rolled out to where you want the dirty water to go. After you have turned off the pump, move the lever to the “BACKWASH” position, and then restart the pump. Most multi-ports have a view glass on them so that you can see the debris coming out of the filter. When the water in the glass is relatively clear, turn off the pump and switch the multi-port valve to “RINSE”, and then run the pump for about 15 seconds. Repeat the “backwash/ rinse” cycle until the water comes out clear. You can then reposition the valve back to the normal “FILTER” position, and you’re all set until the unit needs to be cleaned again. Don’t forget that this process removes water from the pool, so make sure you keep an eye on the water level, and don’t start the cleaning process if the water is already low! Some multi-ports have the “BACKWASH” function, but not the “RINSE’ function. This is also true of multi-ports with a pull up/push down handle. In either of these cases, a 10 second “FILTER” cycle can be used instead of the “RINSE” cycle.
DE filters come in two (2) types. The first makes use of a multi-port for the cleaning and the procedure is exactly the same as cleaning a sand filter (described above). The difference here is that the DE is removed with the dirt, and therefore you have to add more DE after cleaning the filter (sand is not removed when back-washing, so it does not need to be replaced). Because back-washing doesn’t remove all of the DE, you only need to add about 80% of what the filter calls for when new or fully clean. This will assure that the filter doesn’t clog with clean DE.
The second type of DE filter utilizes a handle on top of the filter to shift the internal assembly up and down, reducing the rise in pressure. This type is known as a “bump filter”. To recharge the DE, turn off the pump and open the air valve on the top of the filter for about 5 seconds and re-close it. Next, slowly push the handle down and quickly raise it up again 5 times. Restart the pump, and check to make sure that the pressure dropped more than 2 psi. If it did, you’re in good shape and don’t need to add any new DE to the filter at this time. If it did not, repeat the bumping procedure, remove the plug from the bottom of the filter and run the pump for an additional 30 seconds. Replace the plug, open the air valve on top and run the pump to bleed the air out of the air valve (you’ll be done when water squirts out). Do this whole process twice and you’ll be ready to add about 80% of what the filter calls for when new, just like the other type of DE filter. The general rule of thumb for an uncharged DE filter is to add one (1) pound of DE for every ten (10) square feet of surface area.
Whichever type filter you have, you just need to remember to keep an eye on the pressure gauge and perform the cleanings as needed. This will assure you that you will never encounter poor filtration, cloudy water or costly equipment repair/ replacement. Pretty simple when it only takes a few minutes a month to prevent these issues and have a safe, clean swimming pool!