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Shock Dosage Advice for Swimming Pool Owners
Your pool may need shock dosing for the following reasons:
- Pool has gone green
- Pool is cloudy
- Pool is clean and clear but no sanitiser has been added for some time
1. Pool has gone green
| Possible causes | Remedy |
|---|---|
| No chlorine/bromine in pool. Outdoor pools should have a reading of 3-5ppm. | Shock dose pool (see treatment guide). Consider using chlorine tablets or a chemical dispenser to ensure constant supply of chemical. |
| Ineffective chlorine in pool due to either over-stabilisation (Chlorine lock) or pH too high (At 7.2 chlorine is 66% effective, at 7.8 it is only 22% effective). | To remove stabiliser drain pool water down to 6" below skimmer and refill with fresh water. Shock dose pool (see guide). Consider either increasing backwashing frequency and duration or switching to either a low chlorine system i.e. Nature 2, a non stabilised chlorine or Bromine. Correct pH level. For further advice on the merits of the different systems. click on 'Contact 1st Direct'. |
| Ineffective circulation/filtration - some water not being treated. | Filter may require sand change or backwashing. Pump basket needs emptying. Pump not working effectively. Click on 'Contact 1st Direct' for advice on pumps and filter. Shock dose pool (see guide). |
2. Pool is cloudy
| Possible causes | Remedy |
|---|---|
| Same as above | Same as above |
| Build up of dirt and bather pollution. Particles too small to be filtered out by the sand filter. | Shock dose pool (see guide). Add clarifier to aid filter and "polish" water. |
| Suspended particles due to high pH or high alkalinity. | Correct pH and /or alkalinity. |
3. Pool is clean and clear but no sanitiser has been added for some time
| Possible causes | Remedy |
|---|---|
| No sanitiser has been added i.e. After winter and spring commissioning. Although the pool may appear sparkling clean - possibly due to the use of a good copper based algaecide the algaecide will not kill bacteria and pathogens so a shock dose is necessary to make the pool safe for use. | Shock dose pool (see guide) |
PLEASE NOTE: Before swimming, after a shock treatment, please test the water. Ensure the Chlorine/Bromine & pH levels are safe, before using the pool.
| Grade | Pool Description | Shock Treatment Chlorine |
|---|---|---|
| 1 | Pool apparently clean & clear. 6 ppm No algae growth. Floor at deepest part clearly visible. |
6 ppm |
| 2 | Pool not quite clear. 10 ppm Traces of algae on skimmers. Deep end just visible. |
10 ppm |
| 3 | Pool with noticeable haze. 20 ppm Shallow end floor clearly visible. Deep end not visible. |
20 ppm |
| 4 | Pool slightly cloudy. 30 ppm Shallow end floor not quite visible. | 30 ppm |
| 5 | Pool pale green. 40 ppm Top 3 steps visible but no floors. | 40 ppm |
| 6 | Pool distinctly green. 60 ppm Top steps only visible. | 60 ppm |
Approximate amount of chlorine to give 6ppm and 10ppm
| Pool Size | Litres of 10 % available chlorine Sodium Hypochlorite needed to give: | Grams of 60 % available chlorine Granuales to give: | ||
|---|---|---|---|---|
| Gallons | 6 ppm | 10 ppm | 6 ppm | 10 ppm |
| 5000 | 1½ | 2½ | 300 | 450 |
| 10000 | 3 | 5 | 600 | 900 |
| 15000 | 4½ | 7½ | 900 | 1350 |
| 2000 | 6 | 9½ | 1200 | 1800 |
Ensure that the pump is circulating and that the chlorine is evenly distributed around the pool as concentrated chlorine can cause bleaching of the liner. If the pump is not on try to stir the pool manually. Large quantities of chlorine granules should be dissolved in warm water and then dispersed around the pool.
