Keeping pool water safe and healthful requires careful planning of filter purchases and replacement.

Swimming pool filters are essential to the safe and healthful operation of your pool. If they aren't functioning properly, you may have poor water clarity, creating a dangerous situation in which lifeguards can't see swimmers beneath the surface. And while replacing your filters probably isn't something you think about every day, filter replacement isn't a project that you'll want to put off until urgency sets in. If you do wait, you'll be at the mercy of the filters, and not on your own timeline.

Knowing when to replace your existing filters can be just as important as knowing what types of filters make good replacements.

If you are unsure of the current condition of your filters, take a trip to your filtration room and perform a visual inspection. Several factors may alert you that replacement is necessary. If your filter is of the regenerative-diatomaceousearth or high-rate-sand variety, you should inspect the filter tank for structural integrity. Telltale signs of a failing tank include cracks, corrosion, rust at the seams and water seeping from the seams. Older tanks, manufactured without the tank liners that are commonplace today, may rust from the inside out. This may be evidenced by rust and seeping water. Severely damaged tanks will exhibit this inside-out rust condition with streaks of rusty water leading from a seam hole down the side of the tank. Often, decisions regarding filter purchase and replacement are made by aquatic or athletic directors.

However, the pool operator should never be overlooked as a source of information on the state of a facility's filters, as operators typically work with this equipment more than anyone else. The pool operator may mention such problems as gaps at the seams, rust in backwash, effluent water and failing structural integrity of the tank. By physically pointing out his or her concerns about the filter, the pool operator can provide an even clearer picture of the problem.

The pool itself may show evidence of filter trouble as well. Sand and rust particles may begin to appear in the pool and will settle near filter inlets. The appearance of particles will be most pronounced immediately after backwash of the filters, a problem with two primary causes. The presence of sand in the water is indicative of a failure of the shutoff valve, which is designed to keep water from returning to the pool during backwash. The rust may be from the tank itself or, in severe cases, from the water collection manifold. Keep in mind, however, that small and infrequent amounts of rust in the pool may result from flaking within pipes and should not be mistaken for filter problems. Malfunctioning diatomaceous-earth filters may allow DE particles to escape into the pool water, causing the water to appear milky white and creating a dangerous water-clarity issue. Older, "open pit" DE filters may experience failing structural integrity along the seams of the cement sides and bottom. If the seams fail completely, significant water volume will be lost and the filter will be rendered non-functional, necessitating closure of the pool.

Swimming pools that have not maintained balanced water chemistry over the course of their life produce corrosion or scale buildup on fixtures. This condition may affect filters as well. Running a Langlier Saturation Index on the pool water will confirm whether problems with pH, calcium hardness, alkalinity and temperature are contributing to the condition. This test produces a number on a scale of +3 through -3. Water in the positive range will cause scale formation on pipes; negative numbers indicate a likelihood of corrosion. Perfectly balanced water registers as zero on the scale.

With this test number in mind, inspect your pipes and pump impellers for the buildup of scale or evidence of corrosion. Signs of scale or corrosion could indicate that you already have significant problems with your pipes and filters or that such problems are impending. Scale formation impedes the flow of water through the system and, if left unchecked, can completely obstruct pipes. Corrosion can wear away at pipes and ultimately cause leaks.

One of the final steps to take before determining if and when filter replacement is necessary should be an overall inspection of the face piping, valves and gauges. This inspection may reveal the presence of leaks, cracks or significant deterioration of mechanical aspects of the filter. If you discover significant leaks or the possibility of failing pipes, schedule filter replacement and face piping repair as soon as possible to avoid the possibility of lost water, heat and chemicals, or the complete loss of pool use.

Check with your system manufacturer regarding the expected life span of your filters. Ask for the names of other organizations that use filters similar to yours in pools of like size. Then contact these peer agencies to see how their filters are progressing at a comparable age. If the other agencies are experiencing similar conditions in filters of similar age, your system may be due for replacement. If you decide that you need to replace your filters, the next step is choosing replacements. If your system is more than 20 years old, technology has taken a quantum leap past what you have, and you may need some education.

There are three main types of filters available on the market today: diatomaceous earth, sand and cartridge. Each has its own particular pros and cons, and must be investigated in relation to the individual facility. When you begin to think about new filters, there are several crucial questions that need answering. What is the total volume of your facility's pools? What will your budget allow you to spend? Do you have a particular product in mind?

DE filters use earth containing microscopic fossilized marine organisms to filter dirt and impurities from the pool water. DE systems filter impurities out to the level of one micron, providing cleaner, clearer water than their sand and cartridge counterparts. And though the purchase price is comparatively higher, a regenerative DE system does not require backwashing-providing savings in water, utility (heating of water) and chemical costs. DE filters also take up less space in the pump room. In open pit systems, it is necessary to periodically add DE to the filter. However, if the system is run properly, additions may not be required all that frequently.

One more thing to consider when researching filters is that diatomaceous earth is considered regulated waste in some states, making disposal after its use a concern. An inefficient DE filter, or one that is poorly operated, will require weekly trips to a landfill to dispose of the diatomaceous earth. However, regularly draining the water out of the filter and turning over the DE material-so that collected dirt is on the bottom and fresh diatomaceous earth is on top-can prolong disposal by up to six weeks.

Conventional sand filters cost less than DE filters and also provide clear, sparkling water. Unlike DE filters, sand filters do not require the addition of earth to the filters on a regular basis. Modern sand filters may have PVC or epoxy lining to prevent internal rust and corrosion that have plagued older systems. Among the latest innovations in sand filters are spun fiberglass horizontal tanks, which provide more surface area of filtration for a faster flow rate. Backwashing is still necessary no matter what type of sand filter is selected, but this function can now be performed automatically by an electronic sensor that reads pressure gauges. Cartridge filters are also a relatively inexpensive option and will provide clear water if properly maintained. The cartridge system requires that you remove the filter elements on a regular basis and alternate them with fresh cartridges. The dirty set must then be cleaned by soaking the cartridges in a cleaning solution and scrubbing them off-a labor-intensive approach that requires at least two sets of cartridges. And when the cartridges wear out, replacements must be purchased. However, backwashing of this system is not necessary, resulting in significant cost savings.

The actual process of purchasing filters is not as easy as picking up a catalog and calling a manufacturer. Filters are made specifically for each project; therefore, it's extremely important that your supplier be made aware of your specific needs. Keep in mind when looking at literature regarding filters that some models are made for residential pools only.

During initial contact with your supplier, be sure to make it clear that you have a commercial facility. In fact, before even calling a supplier, make sure you have several pieces of information at the ready, including the total volume of your facility's pools, the required turnover rate for your pools and the square footage available in your filter room for new filters. Let the supplier know what type of system you currently have, whether or not you like it, and why.

If possible, have the company send a sales representative to your facility to see firsthand what you're working with. If the rep notices that you don't have much horizontal space, he or she may recommend a series of vertically stacked cells. You may also be asked to choose between one large filter cell or several smaller ones. One large cell allows for easier maintenance and takes up less space. However, in the event that the lone filter goes off-line, you must close your pool.

With several smaller cells, a single cell can become damaged with little if any disruption in filter function and pool operation, particularly if you've installed some extra capacity in your filter system. You'll also need to answer several additional questions before making your final purchasing decision. Who will install your filters? Do you want a computerized monitoring system for chemicals and temperature? If you choose a sand filter, do you want to automate your backwash function? Will you need to replace a significant amount of face piping, and what type of pipes will serve as replacements? Answers to these questions will significantly impact the cost and timeline for your project.

Finally, don't forget to inquire about technical support, training for your staff regarding the operation of your new filter and any available operation manuals. Having new filters installed isn't enough; you have to be able to operate them effectively.

Once you've decided what to purchase, you'll need to draw up an installation plan. Working with your manufacturer will be crucial during this phase. Because they are customized for each project, filter systems require anywhere from several weeks to several months to manufacture, depending on the model and size. This will play a large role in deciding when your installation will take place. You should also ask your chosen manufacturing company if it has an installation team. If it doesn't, can the manufacturer recommend a contractor in your area, and will they send a technical representative to supervise? Find out whether there will be any impact on the system warranty if you don't use the manufacturer-recommended contractor.

Be sure to check your state's requirements for filter replacement. You may be required to submit blueprints of the change to a state engineer for approval. You may also be required to obtain a construction permit from the state or county government. If so, be sure to allow for several months of document processing before work can begin.

Actual removal of the existing filters is probably the first hurdle you'll have to overcome in the process. Chances are, your system's large size will preclude you from simply removing the filters as a unit. Instead, you'll probably have to cut the tanks into pieces. Even using this option, you'll need a large egress, preferably directly to the exterior of the building. Removing a section of wall or ceiling to allow direct access to the outside may be the best answer. Remember that you'll also be bringing the new filters in the same way, and unlike the old, they can't be cut into pieces.

Once a direct access area has been created, you must ensure that it can be safely secured during and after the workday, perhaps with hatches fitted to the wall or ceiling. This will prevent theft, unauthorized entry to the facility and inadvertent injuries. The large opening will typically dictate that the work be scheduled during warm-weather months.

When preparing for installation, be sure to check whether your pool water supply can be shut off from the filters. If not, you'll need to plan for the draining and refilling of the pool, as well as for the cost of water and chemicals in your project timeline and budget.

For most aquatic facilities, time is money. If your facility isn't open, it can't bring in revenue. Therefore, planning a timeline for installation is a very important issue. How long can you shut your facility down? Do you have a window of time in your calendar that would lend itself to shutdown? Keep in mind that filter replacement is a major task requiring a minimum of a month for demolition, installation and startup. Pre-staging the equipment in the filter area, if space allows, is one way to reduce time spent.

Installation can then begin as soon as demolition is complete. If the current system has multiple tanks, you may explore the possibility of replacing tanks one at a time, thus delaying pool shutdown. Avoid scheduling installation near a holiday, as you will either lose time or pay extra for holiday wages.

When you are selecting shutdown dates, be sure to include as many of your constituent groups in the process as possible-from swim teams to recreational swimmers. If possible, try not to schedule your shutdown in the middle of competitive swim season or the class schedule. Announce your chosen dates in a formal memo sent to each constituent group. Posting the projected shutdown dates at the facility should be done well in advance, as well. Communicate to your patrons that unforeseen setbacks can alter the schedule of a project this large, making the dates tentative.

Filter system replacement is a major task that will require adjustments in operation and planning. But with preparation and foresight on the part of facility staff, the work can be accomplished in a cost-effective, timely and safe manner.