The first step in selecting a chlorinator is to find out your basic water chemistry and have your well water tested. A general mineral analysis will provide a list of the common minerals (calcium, magnesium, iron, manganese, dissolved solids) alkalinity and pH. The pH is important because the higher the pH the more chlorine is required.

How Much Chlorine Should I Plan to Add?

Chlorine is injected in parts per million ('ppm') which is the same as saying milligrams per liter ('mg/L'). For bacteria you want 1 to 2 ppm of chlorine and approximately 10 minutes of contact time. If the water is colder than 50F you may need longer contact time.

For each part per million of iron or manganese you want to inject 1 ppm of chlorine. For each 1.0 ppm of hydrogen sulfide gas (which causes the rotten egg smell in water) you want to inject 2 to 3 ppm of chlorine.

So say you have bacteria and 2.0 ppm of iron. For our example here, we will assume you want to inject 3 ppm of chlorine.

How Do I Know What Size Chlorinator Pump to Install?

The next step in selecting your metering pump is to know how many gallons per minute your well water is flowing at the point where you will be injecting the chlorine. Usually the best place to inject the chlorine is before the pressure tank. Unless you have a variable-speed pump, your water at this point is flowing in approximately the same flow rate every time the well pump turns on. After you use up your reserve in your pressure tank, the pressure switch turns on the well pump and the water begins to flow from the well.

You can easily calculate the flow rate at this point by following these steps:

1. Open any hose bib or faucet until pump turns on.

2. Close hose bib or faucet and let pump fill up pressure tank until it turns off.

3. Using a 1 or 5 gal. bucket, open faucet, collect and measure all water discharged until pump turns on. Let us say this amount is 20 gallons.

4. When pump turns on, immediately close faucet and start timing pump cycle.

5. When pump turns off, record pump cycle time to refill pressure tank in seconds. Let us say this figure is two minutes or 120 seconds.

6. Divide the number of gallons collected in Step 3 by the number of seconds in Step 5. 20 divided by 120 is 0.166

7. Multiply the answer from Step 6 by 60, which comes out to 10.

8. The answer in Step 7 is the average pumping capacity of the pump in gallons per minute (GPM).

Now that you know the amount of chlorine you want to install (3 ppm) and the flow rate of the water stream you are injecting the chlorine into (10 gallons per minute) you are finally ready to calculate the size of the metering pump!

How Strong Should the Chlorine Bleach Solution Be?

Use unscented 5% chlorine laundry bleach and dilute it by adding 9 gallons of water to 1 gallon of bleach. This will give you a solution strength of 5000 parts per million of chlorine.

Metering Pump Sizing

Metering pumps are often rated in the amount of chlorine solution they can pump by gallons per day. They have adjusting knobs so you can pump the full output or turn the pump down to deliver up 90% less than the output.

The formula simple: multiply the flow water (GPM) times the Applied Dosage in Parts Per Million and them multiply this by 1440 (the number of minutes in on 24 hour period). Finally divide this number by the solution strength being used.

10 GPM x 3.0 PPM x 1440 divided by 5000 = 8.6 Gallons Per Day

At this rate you can select a metering pump that can pump 10 gallons per day and adjust the output of the pump to 86% to achieve the desired 8.6 gallons per day. Finally you can test the chlorine residual at the kitchen sink. Your goal should be to have a residual of 0.2 to 0.8 ppm of chlorine. If you find the residual is too high, you can adjust the metering pump down to deliver less or dilute the chlorine solution with more water. If you find the residual is too low, you can make the solution strength stronger by using less water to dilute the solution, or you can turn up the output of the metering pump.