Pool Sand Filter Problems

Swimming is a wonderful way to beat the summer heat. However, appropriate cleaning and maintenance of a pool is crucial. Improper maintenance can lead to allergies and waterborne illnesses. Different types of swimming pool filters are available in the market today, such as cartridge filters, diatomaceous earth filters and sand filters. These filters help maintain the swimming pool water quality, and help remove debris from pool water everyday. In this process, they accumulate grease and dirt, which have to be removed on a regular basis. Filters are seen to encounter various problems during their lifespan. Let us have a look at some of them.

Working of the Sand Filter

Before we head into understanding the different sand filter problems and their solutions, let us have a quick look at how the sand filter works. Pool sand filters comprise a tank or a vessel in which sand is present. Water is pumped into the top of the tank and the internal distributor, thereby causing the pool water to flow through the sand media in the tank. Sand in a pool sand filter (20 silica sand; 45-55 mm) is designed to trap particles in the range of 20-100 micron. Moreover, greater the amount of dirt collected in the sand filter, more the dirt trapped by it.

As the pool water flows through the sand filter media, the debris and dirt in the water gets adhered to sand particles. The water coming out of the sand filter is clean and free of dirt and debris. Filters must be cleaned when the pressure gage shows a reading of 8-10 lbs. The cleansed or filtered water is then sent back into the pool. A pool sand filter runs efficiently for 5 to 7 years, however, after every 3 to 5 years, the sand needs to be replaced. After a certain period of time, the sand filter begins to give way. Some may even incur problems before the expected lifespan is up. Let's have a look at the different problems that can occur with pool sand filters.



Pool sand filters have their set of drawbacks and problems. Moreover, these problems cannot be easily identified as they are not clearly visible. Most of the time, if the sand goes bad, one cannot detect it by simply looking at it. The sand may appear to be in perfect condition, however, the debris from the water does not get filtered. So identifying the problem can be a cumbersome task. Nevertheless, let us have a look at the common sand filter problems.

Sand in the Pool

The most common problem associated with pool having sand filters are sandy pools. Mysterious appearance of sand in pool, a few hours after vacuuming the pool can leave pool owners perplexed. There can be several reasons for sand accumulation in the pool. Let us have a look at them one by one.

➢One primary reason for sandy pools are bad or cracked laterals. One can observe that a large amount of sand is being dumped into the swimming pool via the pool returns. This happens when the filter laterals have cracked. To solve this issue, one will have to empty the sand tank and check the laterals for breakage. Broken laterals have to be replaced and then the tank must be refilled with fresh sand.

➢The pool water may also appear muddy when the filter is not appropriate for the pool. An undersized or oversized pool filter may also cause filtration problems.

➢If the sand added to the filter is of very fine grade, then it is bound to seep into the pool water. Thus, ensure that the sand used in the filter is of the right grade for your filter and pool. Mostly 20 grade silica sand; 45-55 mm, is recommended. Check with the manufacturer's instructions to be completely sure.

➢While vacuuming the pool, one should vacuum to 'waste', such that the pool gets drained.

➢If the sand in the filter hasn't been changed for over three years, then it's most likely the sand particles have got eroded and reduced in size with time, such that they are now small enough to flow right through the laterals and into the pool.

➢Sometimes, right after replacing the sand in the pool filter, the pool becomes muddy with sand particles. This happens because fine sand particles get free and enter the pool water. However, the sand in the filter settles within the next week, and this problem will be solved.

➢Shorter and frequent backwashing cycles can also result in sandy pools. Backwashing is a standard procedure carried out during pool maintenance, to flush out the dirt and debris trapped in the sand filter. The gauge on the filter will indicate with its high pressure reading, as to when the pool filter should be backwashed. During a backwash cycle, the water flows in the reverse direction, thereby causing the dirt to flow out through the waste line of the filter. Backwashing should be done until the water runs clear in the valve's sight glass. This may not take more than a couple of minutes.

➢Usually, one will have to backwash only once in 30 to 40 days, however, when there is a problem with the sand filter, the gauge may indicate high pressure within a week or two, since the previous backwashing. Short filter cycles imply that the filter sand is clogged with the dirt and sand and needs to be replaced. It may also be due to an undersized filter. So check and find out if the filter is of the appropriate size with respect to the size of the pool or not. A proper sized filter should only take about 6 to 8 hours to filter the pool water.

➢In another case, if the sand returns to the pool right after backwashing, then a displaced air tube can be the cause. The filter will have to be opened to see if the air tube has been displaced from its position. Checking air tube's position does not require the removal of the entire sand in the filter. A displaced air tube can cause air to pass through the filter, which in turn results in a channeling effect (formation of an actual channel down the side of the filter). Thus, dirt and debris gets past the filter and into the pool water. So even though the sand filter is working just fine, a displaced air tube can cause sand to accumulate in the pool.

Sand Filter Leakage

One may find water on the ground and around the filter, if the filter is leaking. It is unusual for pool sand filters to leak, however, if they do leak, the leakage mostly occurs at the multi-port interface. The O-ring or gasket situated at the base of the multi-port valve may get damaged. Due to this damaged part, the water returns to the pool unfiltered. Sometimes, minor adjustments to the handle can solve this problem. However, this is a temporary solution and replacement is a better option in the long run.

Sometimes, the plastic split nut may also be damaged and may need replacement. If the leakage is around the central portion of the handle on the valve, then the replacement of a Teflon washer and a spring is necessary. The drain plug can also leak if not secured properly and tightly. Filters tanks may crack and may also require replacement. Leakage can also occur if the filter has been fitted incorrectly. Even simple components like nuts, washers, etc. if not fitted correctly can conduce to leakage in the filter apparatus.

Cloudy Pool Water

At times, it may so happen that the water appears cloudy or muddy in spite of good flow. In such a case, one must test the water chemistry. Algae, body oils from bathers and calcium deposits in the sand, can also be a reason for frequent backwashing requirement. Calcification occurs if the pH of the water is very high. Moreover, low free chlorine levels give rise to algal growth. Thus, it is extremely important to maintain the chemical balance of the pool to avoid all these unwanted problems.

To confirm algal growth, just sweep the pool floor with a broom. If the broom surface appears sticky, then it's algae, but if the particles get disturbed quickly it's more likely to be sand. Algaecides will be required to get rid of the algae. The chemical balance can be checked using a water chemistry test kit. If water chemistry is not the issue, then one must check the backwash valve and make sure the water is not bypassing the filter. If all these tests are negative, then its confirmed that the sand in the filter has gone bad and needs replacement.

Replacing Sand in a Sand Filter

To replace the sand, one must first turn off the filter. Never try doing anything while the filter is on. The next task is to empty out all the existing sand from the filter, after unscrewing the different nuts and bolts on the filter. One method is by spreading a tarp beneath the filter drain assembly. Next, remove the entire assembly, turn the pump on and step aside. The water pumping through the sand filter will cause the sand to be removed via the drain hole.

Another method is by removing the drain plug and allowing the filter to drain for next few hours or days. Then, the top dome or multi-port valve is removed, after which one must gently twist the pipe out of the way to be able to scoop the sand. While scooping, one must be careful not to break the filter laterals, which are located under the sand, at the bottom of the tank. Laterals allow pool water to exit the tank and flow back to the pool. The sand beneath the laterals can be removed by using a hose. Once the tank has been emptied, fresh sand can be filled, however, make sure no sand enters the manifold pipe.

Backwashing a sand filter once every month is essential to get rid of the collected debris. Moreover, the sand bed in the sand filter ought to be replaced after every three years. Ensure proper pool maintenance, as regular pool maintenance throughout the year, irrespective of the pool type, increases the life of the swimming pool filters and reduces overall costs and hassles!