Water treatment for pools: chlorine shock

Swimming pool waters usually undergo continuous chlorine shock treatment and must maintain a residual chlorine level between 1-3 ppm. Nonetheless, certain environmental conditions or filtration system failures can cause algae blooms. Therefore, when this occurs, shock treatment is necessary.

“Chlorine Shock” treatment

The table below is a guide for shock-type treatments:

Degree	Pool description	Water treatment for pools: chlorine shock
1	The pool has a clean and clear appearance. There is no algae growth.	6 ppm.
	The floor in the deepest part is visible.
2	The pool is not very clear. Traces of algae in the skimmers.	10 ppm.
	The pool bottom is barely visible.
3	Pool with appreciable turbidity (mist).	20 ppm.
	The bottom of the lower floor is a little bit visible.
4	The pool is slightly cloudy. The bottom of the floor is barely visible.	30 ppm.
5	The water is pale green. The floors are not visible, only the first three steps.	40 ppm.
6	The water is purely green, with only the first few steps visible.	60 ppm.

How do you estimate how much chlorine to add to a pool?

There are two ways to apply chlorine shock: one is in the pool, and another is through recirculation through a chlorine dispenser.

CALCULATION OF THE VOLUME OF CHLORINE SOLUTION TO ADD (THE SAME POOL):

These are the necessary data:

• Vp = volume of the pool in liters
• DC = dose of chlorine to apply in ppm ≅ mg/L
• C = concentration of sodium hypochlorite % by weight
• ρC = density of the chlorine solution in kg/l

So, we will estimate the volume of sodium hypochlorite VC that we must add to the pool:

• VC = volume of sodium hypochlorite in solution to add to the pool

*1ppm. by weight = 1 kg / ≅ 1 mg / l, since the density of water is approximately equal to 1*

Example

Vp = 300.000 liters

DC = 30 mg/l

C = 12,5 %

ρC = 1.24 kg / l

VC = (0,0001 x 300,000 l * 30 ppm) / (12.5 % * 1.24 kg/l) = 58 L

CALCULATION OF THE VOLUME OF CHLORINE SOLUTION TO ADD IN RECIRCULATION:

First, in the case of recirculation, it is to be pointed out that, as a rule (example: 10 state standards), a pool must recirculate at least its entire volume in six hours, but if it is a pool for children, it is at least two hours.

Also, you must dose the 58 L in a desired period that does not exceed that of the total recirculation of the pool. For example, if the water recirculates its entire volume in 6 hours, you can dose 58 L per 6 hours and must set your dosing pump at 9.6 l/hr.

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