Pool Clarity and Backwashing

Clarity of water is one sign of the condition of the pool. If the pool is cloudy, this could be due to a number of things.

Pools hPool cleared with flocculentsave filters fitted which remove small particles that are in the water. Most filters either use sand or glass media to achieve this. The water is pumped out of the pool through the bottom and from the water overflowing into the skimmers. It is then pumped through the filter where the media traps particles in the sand and gravel and returns clean water to the pool. If an automatic pool chemical dosing system is used, chlorine is added to the water passing through if required.

The pool filter system should be backwashed once or twice a week to remove material that has built up.  You can usually see how dirty this water is through a clear bit of pipe on the drain side. Backwashing achieves two things: firstly it cleans and clears the filter of debris and secondly you add fresh water to replace any that was drained.   This is important because dirt in the filter continues to react with free chlorine in the pool and if very dirty free chlorine will be drained quickly.

However backwashing too often can also cause problems.  The media needs time to settle after a backwash to improve its effectiveness in trapping smaller particles. A pool backwashed too often (daily or more) will end up cloudy because the filter cannot perform its task properly.

Even with a good filter that is backwashed correctly, the water can still have tiny bits. These can barely be seen except when the pool is empty or there are lights and this bits can be seen “dancing” in the light. These bits are too small to be trapped in the filter and over a period of time will build up giving the pool a cloudy appearance.

These can be eliminated by the use of flocculants.  Flocculants are products that make these tiny particles stick together and become bigger particles that the filter can then remove. There are two types that can be used:

  • Flocculent tablets such as Goldifloc are placed in the strainer basket and break down slowly
  • Liquid flocculent such as Poolclear which can either be added continuously as very slow dose rates by a pump as used in commercial pools. This binds all these tiny particles together so they can be removed

It is recommended that the filter is backwashed a day or so after the use of flocculent.  Excessive use of flocculent can cause the filter media to stick together and not be as effective.

The photo above shows a pool that has been treated with flocculent and how crystal clear it is: