Residential Pools and Spas

Cleaning swimming pools after storms and floods

June 11, 2017

David Lloyd of International Quadratics has provided some advice on cleaning up and treating swimming pools after storms and floods.

Cyclones, storms and flooding has several effects on swimming pools, including the following:

• Dirt and debris washed into the pool
• Phosphates introduced into the water
• Dilution of the chlorine causing algae to form
• Dilution of the salt and mineral content of the water

Below are some quick tips for handling the situation.

Step 1. The first step is to clean the pool of dirt and debris. Remove any large debris such as branches etc, empty both the skimmer and pump basket. In the case of the water being very dirty such as when soil has been flushed into the pool, a heavy duty floc may be required. Follow the label instructions of the floc you are using and then vacuum the pool to waste. See below for important information relating to keeping the pH high for flocs to work properly.

Step 2. Test and re-balance the pool water including the addition of salt and minerals where
required.

Step 3. Shock dose the pool.

Step 4. Add the required dose of phosphate remover to remove unwanted phosphates.

Step 5. In case of cloudy water use a clarifier.

Step 6. Add a winteriser treatment or maintenance algaecide.

Flocculants and coagulants

This might be an appropriate time for a refresher course on flocculants and how they work.

The terms “flocculants” and “coagulants” are synonymous with each other; however the process of clearing cloudy/dirty pools is in fact a two-stage process involving both coagulation and flocculation.

Turbidity (or cloudiness) of water is caused by fine particles suspended in the water. These particles are typically smaller than two microns and will normally pass through the filter system. They are of low density and will therefore be suspended in the water. Most particles are negatively charged and repel each other.

In order to remove these particles it is first necessary to add a flocculent (positively charged) which will coagulate the fine particles into larger “flocs” by neutralising the negative charge, allowing the particles to come together and form a floc.

Some flocs will be “light flocs” which will tend to remain suspended in the water or even rise to the surface of the pool and are then caught on the filter bed. Algae and organic matter may form lighter flocs.

Soil, dust and clay, being denser will form heavier flocs which will sink and form sedimentation on the floor of the pool and this should be then vacuumed to waste. The type of flocculent used will also dictate if a light or heavy floc is formed. Aluminium based flocs such as poly aluminium chloride (PAC) or Alum will form a heavy floc which settles on the bottom while some Cationic Electrolytes and natural flocs  will form light flocs and tend to be caught by the filter.

In the case of a really dirty pool, for example after large storms or in the case of Cyclone Debbie, we would recommend the use of a heavy floc such as liquid PAC or powdered/granular Alum.

The importance of pH

It is important to note that aluminium flocs only work at a high pH so you must first raise the pH of the pool to at least 8 when using Alum or 7.8 when using a liquid PAC based product.

Alum has a low pH and will immediately reduce the pH of the water after addition.

Common practice when using Alum is to raise the pH to 8+ using Soda Ash and then add 2 to 4 kg of sodium bicarb (buffer) at the same time as adding the Alum. This will compensate for any drop in pH and also increase the Total Alkalinity.

When using a PAC base product, the pH should be raise to at least 7.8. However, the effect on pH of the water after addition is significantly less than that of Alum so further reduction is usually unnecessary. It should also be noted that Alum contains typically 8 per cent Al2O3 (the active floc) while PAC may contain 23 per cent Al2O3 (three times stronger).

Floccing points

Some important points to note when flocking pools are:

• It is difficult to floc live algae. If there is any evidence of the presence of algae, super chlorinate using liquid chlorine (this also assists in the raising of the pH).

• If Phosphates are present the floc may be partially used up floccing the Phosphates and slow up the process of clearing the pool.

• High TDS levels or Salt will also slow up or prevent efficient flocculation. The use of a fast floc which has an inbuilt accelerator may compensate for this.

• Most Flocs are incompatible with DE or cartridge filters. Cartridges should be removed before recirculation and mixing of Flocs; DE filters should be set on ‘recirculation’ or ‘By-Pass’.

One last tip – after vacuuming and rebalancing the pool water place a clarifier in the skimmer basket to really polish the water and leave it crystal clear.

For more information contact International Quadratics.

Beware emptying pools

No matter how bad you think the water might be after a cyclone, be aware that flood water will have made the ground conditions around the foundations of the pool very wet. Pools should not be drained until ground conditions have dried to at least the depth of the pool as the entire shell of the pool (fibreglass or concrete) can “pop” out of its original position with the change in hydrostatic pressures.



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