The call comes in — the pool’s filtration system is on the blink. What to do? In this troubleshooting guide, some common symptoms of ailing filters are presented with practical tips on how to bring them back to good health.Before you dive in, please take note of this general rule: When assessing an operating filter’s performance, check the pressure gauge first to make sure it’s working properly. Some techs carry an extra gauge, and will test it on the filter to ensure it’s working well. Others suggest tapping the face or casing of the gauge firmly to make sure the needle is not sticking. A gauge that fails to indicate a rise in pressure not only compromises your ability to monitor filter cycles, but it also can be hazardous.

Keep in mind as well that many symptoms of a malfunctioning filter system can be brought on by inadequate running time. The first step in troubleshooting is to simply be sure the system is running enough to stay on top of filtering demand.

Finally, it is important to point out that these guidelines are for general information only. You should always consult manufacturer literature for specific recommendations and operating guidelines for each filter model you encounter in the field.

Symptom: Reduced flow of water through the filter

General tips: As dirt accumulates on the filter media, water flow is restricted — and pressure within the tank rises. When the pressure rises to a level specified by the manufacturer, it is time to backwash a sand or DE filter, or to clean the elements in a cartridge filter. The ranges of operating pressures for filters vary, depending on the type.
Gradual pressure rises are normal in the course of any filter cycle. If the rise in pressure is fairly consistent, then normal backwashing will suffice. If pressure begins to rise more rapidly than normal (called short cycling) or if the automatic cleaner stops working, it’s time to look at the filtration system.

Sand filters: A typical range for high-rate sand filters, for example, may be 10 to 15 pounds per square inch at the beginning of the filter cycle (that is, the period between routine backwashings or cleanings) on up to 20 to 25 psi when backwashing is required.

DE filters: Some filter systems — mainly DE filters on large commercial installations or large high-rate sand filters — have pressure gauges installed on both the influent (inlet) and effluent (outlet) lines. As the media become clogged with dirt, the influent pressure will become higher than the effluent reading.
When the differential between readings reaches a specified level, it’s time to backwash the filter.

Symptom: Low flow rates in the system

Proper flow rates: If you get a low reading with a flowmeter, but a high reading on the pressure gauge, something is restricting the flow. It could be one of several issues: a plugged filter, closed jets in the pool, or an issue with the heater. In rare cases, this problem is caused by plugged piping or a broken piece of equipment lodged upstream of the filter.

Low flow rates and low pressure could be a restriction or air leak in the suction piping or problems with the pump.Generally, the maximum flow rate through a 1½-inch PVC pipe is 55 to 60 gallons per minute. Through 2-inch plumbing, it should be 95 to 100 gpm. These figures are based on a standard hydraulic specification of an 8-feet-per-second maximum velocity, although many prefer 6-feet-per-second or less through the suction line.

Clogged baskets: A drop in the return flow may be traced to a clogged pump strainer or skimmer basket, so clean the baskets. Clogged impeller vanes also will reduce the return flow; disassemble the pump and clean the impeller.Pump: If both flow and pressure readings are low, the pump may be undersized — or you may have a plugged pump impeller or lint trap. Pump or motor trouble can lead directly to filtration problems, so keep that in mind as you troubleshoot the system.

Symptom: Inadequate filtering action.

Cartridge filters: Poor filtration without a rise in pressure may indicate torn or worn-out cartridges that are allowing water to pass through without filtering. Replace cartridges as needed.

Sand filters: Charging: In a sand filter, if the media have been charged improperly or inadequately, channels may have formed in the sand and gravel bed and may be allowing water to pass through unfiltered. Look for evidence of channeling or tunneling — and recharge the filter, if necessary.

Mudballs: If the unit has not been backwashed thoroughly, mudballs may have formed on the surface of the sand bed, thereby limiting filtering action. Or, in extreme cases, the sand may have calcified and will no longer filter out dirt. Look for mudballs or evidence of calcification and, if found, backwash or remove the old sand and recharge the filter as necessary. With proper maintenance, filter sand normally has to be replaced every four to five years, though it may last longer.

DE filters: Coagulation: Poor filtration from these units often results from coagulation or solidification of the DE. If you see hardening of the DE cake, remove and clean the elements per the manufacturer’s instructions and recharge the filter with fresh DE.

DE introduction rate: If DE is fed to the unit by slurry feeder, the unit may not be feeding enough DE into the filter to adequately coat the septa. Conversely, an inconsistent filter cake may result from feeding DE too quickly into a skimmer when recharging the system. The trick here is to watch DE introduction rates and adjust them as needed.Coating the filter: If you have an over-sized DE filter or an under-rated pump, there may be inadequate pressure within the filter to properly coat the septa. Here, you need to check the manufacturer specs and replace equipment as needed.

Sand and DE filters: Backwashing: If backwashing isn’t performed frequently enough or for adequate periods when it is performed, the media will not be cleaned sufficiently. It always pays in these cases to follow manufacturer specs — and to avoid shortcuts that may turn into headaches later on.

Backwash lines: Watch out for inadequate or plugged backwash lines that might not be allowing sufficient flow out of the filter during backwashing. Although rare, if a portion of the backwash discharge is retained in the tank because of inadequate flow, the backwash line will clog over time with caked media. To address this, check the lines for clogs and clear as necessary.

Symptom: Short cycle between backwashes

General tips: Flow rate: Most often, short filter cycles indicate excessive flow rate through the filter. This indicates that the filter may be undersized or that the pump may be too powerful for the system. If you’re comfortable with filter-sizing equations, do a quick check of the numbers to be sure equipment is sized correctly. A manufacturer’s technical representative should be able to help. Once that’s all fine, install a properly sized system.

Contaminants: In other cases, short filter cycles suggest large amounts of dirt, debris, body oil, lotions, hair or algae. Very high bather loads (or pet usage or excessive fertilizing of plants and lawns) lead to overworked filters. Discuss your observations with the pool owner to see if changes in routines are necessary. Backwash the filter as needed.

DE filters: Clogging of the vertical grids in a DE filter — whether by rust, calcium buildup or soda ash — may increase the pressure and compromise effective filtration. If you suspect this problem, clean the filter elements and check for clogging of the fine nylon mesh covering the septa. Treating the septa to a light acid wash and hosing with a strong stream of water will usually relieve the problem.

Sand and DE filters: With sand filters, and DE filters to a lesser extent, you can get into trouble when soda ash or coagulants are fed into the skimmer too fast.

In these caes, some chemicals do not have sufficient opportunity to dissolve. Rather than passing through the bed in solution, the chemicals clog the media and raise the pressure. The key is to introduce these agents more slowly, or dissolve them before introducing them to the skimmer.

Note: Alum should never be used with a DE filter. It will only solidify the filter cake.

Symptom: Sand or DE is entering the pool

Sand and DE filters: One suspect with sand- or DE-clouded water is the push-pull valve. If it is left in an intermediate position, media can flow back into the pool. If this obvious answer doesn’t suffice, you’ll need to look for solutions inside the tank.

Sand filters: Broken laterals or undersized sand that is smaller than the manufacturer’s recommendation are common culprits here. Replacement of components and/or the sand itself is recommended.

DE filters: The first suspect is torn or worn-out septa, which will allow DE to flow into the pool. The nylon mesh on the septa can be repaired, depending on how large a hole or tear is present. And think small: A hole the size of a pencil lead will allow DE to escape.

Tip: Always check the points where the mesh is sewn to the frame of the grid. Even slight unraveling will allow DE to enter the pool.

DE may be migrating back to the main drain or skimmer when the pump shuts off. Excessive flow rate through the filter also can force sand or DE into the pool. Again, filter and pump sizing should be checked. A damaged internal airbleed also will allow DE back into the pool.

Make sure there is a check valve between the filter and the pump if you open up the DE filter. DE will flow back through the pump into the pool through the skimmer.

Symptom: There’s a build-up of air

General tips: Firstly, air present in the filter tank can compromise filtering action. In sand filters, it’s a prime suspect in channeling. In DE units, it may disrupt the filter cake.

More importantly, however, air pressure buildup in a filter can be hazardous. Anyone who has seen a filter fracture knows the potential for damage and possible injury.

Air in the filter tank: If there’s a problem with air in the tank, check for hairline cracks or leaks in plumbing connections on the suction side of the pump. A low water level in the pool is another suspect: Air may enter through the skimmer.

Releasing the air: It’s always important to release any air present in the filter tank. (Note: Many filters are equipped with automatic venting devices.) Not only will the presence of air inhibit good filtration, it also can increase the hazardous pressure.

Air is easily released by opening the pressure release valve and allowing the air to escape. When a steady stream of water comes out of the valve, then all of the trapped air has been released.

Pool & Spa News thanks Hayward Pool Products for its assistance in preparing this guide.