How Do You Add Chlorine to a Tank?

Adding chlorine to a tank, particularly a water storage tank, is usually done to disinfect it. Here's how you do it:

1. Calculate the Tank Volume:

First, you need to know the volume of the tank in gallons. This is crucial for accurate chlorine dosing. For a cylindrical tank, the volume can be calculated as:

Volume = π (radius)^2 height

Where:

π (pi) ≈ 3.14159
radius = diameter / 2
height = height of the water in the tank

For other tank shapes, use the appropriate volume calculation formula. If you don't have the tank's dimensions, consult the manufacturer's specifications.

2. Determine the Chlorine Dosage:

The standard recommendation for shock chlorination is to achieve a chlorine concentration of approximately 50 parts per million (ppm). A common guideline uses household bleach (typically 5.25% chlorine):

General Rule: Use 1 gallon of non-scented, NSF-approved household bleach (5.25% chlorine) for every 1,000 gallons of water.
Smaller Volumes: Use 1 quart of bleach for every 250 gallons of water.

3. Calculate the Amount of Bleach Needed:

Use the following formula to calculate the amount of bleach required:

Bleach (gallons) = Tank Volume (gallons) / 1000

For example, if you have a 500-gallon tank:

Bleach (gallons) = 500 / 1000 = 0.5 gallons (or 2 quarts)

4. Adding the Chlorine:

Safety First: Wear appropriate safety gear, including gloves and eye protection.
Pre-Mix: Ideally, dilute the calculated amount of bleach into a bucket of water before adding it to the tank. This helps distribute the chlorine more evenly.
Pour into the Tank: Pour the diluted bleach solution into the tank. It's best to pour it near the inlet or while the tank is filling to help mix the chlorine.
Mixing: If possible, use a pump or other means to circulate the water in the tank to ensure the chlorine is thoroughly mixed.

5. Contact Time:

Allow the chlorinated water to sit in the tank for at least 12-24 hours to effectively disinfect it.

6. Dechlorination (Optional but Recommended):

After the contact time, you will need to dechlorinate the water before use or disposal, unless the low residual chlorine is acceptable for the intended use (irrigation, etc). If the water will be used for drinking, it must be dechlorinated or allowed to sit until chlorine dissipates naturally. You can dechlorinate using:

Sunlight: Letting the water sit exposed to sunlight can naturally dissipate chlorine over several days.
Activated Carbon Filter: Running the water through an activated carbon filter will remove the chlorine.
Chemical Neutralization: Chemicals like sodium thiosulfate can neutralize chlorine, but require careful calculation and handling.

Example Scenario:

You have a 1500-gallon water storage tank.

You need 1500 / 1000 = 1.5 gallons of bleach.
Dilute the 1.5 gallons of bleach into a larger container of water.
Pour the diluted solution into the tank.
Allow it to sit for 12-24 hours.
Dechlorinate if necessary.

Important Considerations:

Type of Bleach: Always use unscented, NSF-approved household bleach containing 5.25% chlorine (or the equivalent concentration for other bleach products; adjust the calculation accordingly).
Water Source: If your water source is contaminated, you may need to repeat the chlorination process or consider other disinfection methods.
Local Regulations: Check local regulations regarding water disinfection and disposal of chlorinated water.
Alternative Disinfectants: Other disinfectants, such as chlorine dioxide, are available and may be more suitable for certain applications. Consult with a water treatment professional.