Pool Sand Filter Problems

Gardenerdy Staff Sep 24, 2018
Sand filters are devices that keep the swimming pool water free of debris and dirt, and are essential for the maintenance of the pool water. Maintenance of sand filters requires a standard check.
Swimming is a good way to beat summer heat. Proper cleaning and maintenance of a pool is important. Lack of regular maintenance can lead to allergies and waterborne illnesses. Different types of swimming pool filters are available in the market today, like cartridge filters, diatomaceous earth filters and sand filters.
These filters help maintain the swimming pool water quality, and help remove debris from the pool water. In this process, they accumulate grease and dirt, which has to be removed on a regular basis. Filters encounter various problems during their lifespan.

Working of Sand Filters

Before we head to understanding the different sand filter problems and their solutions, let us have a quick look at how sand filters work. Pool sand filters comprise a tank or a vessel in which sand is present. Water is pumped into the tank and the internal distributor, thereby causing the pool water to flow through the sand medium in the tank.
The sand in a pool sand filter (20 silica sand; 45-55 mm) is designed to trap particles in the range of 20-100 microns. Moreover, greater the amount of dirt collected in the sand filter, more is the dirt trapped by it.
As the pool water flows through the sand filter medium, the sand particles accumulate debris and dirt around them. The water coming out of the sand filter is clean and free of dirt and debris. Filters must be cleaned when the pressure gauge shows a reading of 8-10 lbs.
The clean water is then flown back into the pool. A pool sand filter runs efficiently for 5 to 7 years if maintained well. After every 3 to 5 years, the sand needs to be replaced and the sand filters need to be cleaned regularly.

Problems with Pool Sand Filters

Sand in the Pool

The most common problem that sand filter pools face is the accumulation of sand in them, a few hours after vacuuming.


◘ The main reason for sand in pool is bad or cracked laterals. A lot of sand is being dumped into the swimming pool through the pool returns. This happens when the filter laterals have cracked. To solve this issue, one has to empty the sand tank and check the laterals. Broken laterals have to be replaced and the tank must be refilled with fresh sand.
◘ Pool water may appear muddy if the filter is not proper for the pool. Under or over-sized pool filter also causes problems.
◘ If sand added to the filter is very fine, it seeps into the water. Ensure that sand used is of the right grade for the filter and pool. 20 grade silica sand; 45-55 mm, is recommended. Check with the manufacturer's instructions also.
◘ While vacuuming, the pool should be drained.
◘ If sand hasn't been changed for over three years, it is likely that it's particles have eroded and reduced in size, small enough to flow through the laterals 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 become free and enter the pool water. However, the sand in the filter settles in a week, and this problem gets 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 that it needs to be replaced. It may also be due to an undersized filter. So check to see if the filter is of the correct size. A filter should only take about 6 to 8 hours to filter the pool water.
◘ If sand returns to the pool just after backwashing, a displaced air tube can be the cause. The filter has to be opened to see if air tube has been displaced from its position. This does not need the sand to be removed. A displaced air tube causes air to pass through the filter, giving a channel effect (forming of actual channel at the side of the filter).
Thus, dirt and debris gets past the filter and into the pool water. And even when 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 leaks. It is not usual for the sand filters to leak. It occurs mostly at the multi-port interface. The O-ring or gasket at the base of the valve may be damaged and water returns to the pool unfiltered. Minor adjustments to the handle solves the problem, but replacing is a better option.
Sometimes, the plastic split nut may be damaged and need replacement. If the leakage is around the central portion of the handle on the valve, replacement of a Teflon washer and a spring is necessary. The drain plug can also leak if not secured properly.
Filter tanks may crack and 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 cause leakage in the filter apparatus.

Cloudy Pool Water

At times, it may happen that the water appears cloudy or muddy. One must test the water. Algae, body oils from those bathing in the pool and calcium deposits in the sand, can be reasons for the need of frequent backwashing. High pH of water causes calcification.
Low free chlorine levels give rise to algal growth. It is important to maintain the chemical balance of the pool to avoid such problems.To check for algal growth, sweep the pool floor with a broom. If the broom surface is sticky, there are chances of algal growth. Algaecides can help in getting rid of 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 that the water is not bypassing the filter. If all these tests are negative, then it is confirmed that the sand in the filter has gone bad and needs to be replaced.

Replacing Sand in a Sand Filter

First turn off the filter. Never try anything while the filter is on. Empty out the existing sand, after unscrewing the nuts and bolts on the filter. One method is spreading a tarp below the filter drain assembly. Remove the assembly, turn the pump on and step aside. Water pumping through the sand filter will cause the sand to be removed from the drain hole.
Another method is to remove the drain plug and allow the filter to drain for a few hours or days. Then, the top dome or multi-port valve is removed, after which the pipe is gently twisted out 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 the pool water to flow out of the tank and flow back into the pool. The sand beneath the laterals can be removed, using a hose. Once the tank has been emptied, fresh sand can be filled. In doing this, make sure that 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 filter needs to be replaced after every three years. Regular pool maintenance increases the life of the pool filters. Moreover, it reduces the overall cost incurred and the hassles too!