How to adjust chlorine levels in your Chlorination System

This article explains how to adjust chlorine levels in a chlorination system, so your flow switch can add an accurate amount of chlorine to your system.

CHLORINE:  LIQUID CHLORINE IS THE ONLY TYPE THAT CAN BE USED IN THIS SYSTEM. NEVER USE SOLID TABLETS!  Pool chlorine is about 10% strength.  I use this exclusively.  It is readily available from a pool supply in those yellow 2.5 gal containers, or at Home Depot or Lowe’s in 1 gal jugs.

I do not recommend using household bleach from the grocery stores as there is no way to know what the ingredients are.  If this is all that is available to you, make sure that you get the “plain Jane” kind with NO additives.  Household bleach is ONE HALF the strength of pool chlorine, or about 5%.

TRANSPORTING:  CAUTION!  ALL CHLORINE (NaOCl-Sodium Hypochlorite) SOLUTIONS ARE STONG AND CORROSIVE.  TO TRANSPORT IN YOUR VEHICLE, PICK UP ONE OF THOSE CHEAP PLASTIC “TOTES” AND PUT THE CHLORINE JUGS INTO THE TOTE.  IF ANYTHING SPILLS OR LEAKS, THE PLASTIC CONTAINER WILL PREVENT DAMAGE TO YOUR VEHICLE.

You will need the 30 or 35 gal solution tank.  It will use a MIXTURE of chlorine + water.

ALL RATIOS BELOW USE THE 10% POOL CHLORINE.

CAUTION:  CHLORINE CAN SPLASH AROUND.  WEAR EYE PROTECTION!!  AND OLD CLOTHES!  IT WILL BLEACH THEM OUT IF IT SPLASHES ON YOU!

PRIME YOUR PUMP USING ONLY WATER that you have MEASURED so you can set up your ratios as described below. 

Make your injection line only long enough to go to the injector fitting with a little slack so there is no binding or strain..  Hold the injector line UP and AWAY FROM YOU.  Let your pump run at MAX until all the air is pumped out of the line, turn the pump OFF and connect the injector line to the injector fitting.

In a 30 or 35 gal solution tank, 1 inch = about 1 gal.

I like to make simple ratios of water + chlorine, so, in my mind I use 10 gallon increments.  I divide the tank in my mind into 1/3 increments and begin with 1/3 of the tank (10 gal) as my initial mixture.

10 gallons = 10 inches on the tank, which can be “eye-balled” easily as 1/3 of the tank, or measure on the outside of the tank.

If your well water has little or no objectionable odor, you should begin with a small amount of chlorine: 1/2 gal of pool chlorine plus 9 1/2 gal of water for your initial mixture.  Remember, we begin with a 10 gal mixture in a 30 or 35 gal tank when starting up the system. A 10 gal mixture will operate your system for at least 10 days and gives you the flexibility to adjust the mixture.

In wells with a mild odor or heavy iron, I will begin with a 1:9 ratio (1 gal of chlorine + 9 gal water = a 10 gal mixture = 10 inches in the tank).

For wells with a strong, obnoxious sulfur/rotten egg odors I will normally begin with a 2:8 ratio (2 gal of chlorine + 8 gal water = a 10 gal mixture = 10 inches in the tank).

Either way you choose is OK because, after testing the actual residual, you will be able to change the ratio quite easily..  This is how you will start up the system

… WITH ONLY A 10 GAL MIXTURE IN THE TANK.

After starting up your system test the residual from the test bibb located downstream from the Retention Tank and upstream from the Carbon Filter.  Plan on testing this residual DAILY for the first week. Adjust the SPEED as necessary to achieve a nice yellow color with your OTO test kit (about 1-3 ppm).  As you make adjustments with the  SPEED (upper) knob on the pump, you will get a feel for how it works and it will make sense to you.

If your chlorine injector pump has a single adjustment knob, start at 50% and adjust accordingly. 

If yours is a dual control pump, the lower, large knob is the pump STROKE and it is always set at 100%. 

The upper knob is much smaller.  It controls the SPEED.  You start out at 50% and then adjust up or down, depending on the chlorine reading. This is tested at the faucet which you will pipe in near the top of the retention tank on the DOWNSTREAM side. 

Checking the Chlorine Residual:  You will need to pick up a chlorine test kit from Lowe’s or Home Depot or the pool supply store.  Get the cheapest one you can because you measure ONLY the chlorine residual.  I recommend the OTO test kit (the yellow stuff).  This makes life very simple.  If the residual measures a nice yellow color, the residual is just right.  If it is very light yellow or clear, it probably means your pump has lost its prime.  Re-prime according to the pump manual; run the water out the top of the RT (from the test bibb) for about 15 min and test again.  If the residual is a light yellow, turn the SPEED up by 30-40%.  If the residual is a dark yellow or orange, turn the SPEED down 30-40%.  Test again the next day.  Make adjustments as necessary, testing each day, until the residual gives you a nice yellow color.