Thank you for contacting us. You wrote:
“How much bleach should I add to an 8,000 gallon tank if it is a 8.25% solution vs a 5% solution (clorox)? My water tested positive for coliform bacteria and I want to get rid of it in the storage tank so I can re-test the water.
For shock chlorination we recommend a 50 PPM residual. Let the water sit for at least 12 hours and re-test the water for chlorine residual. If the chlorine is less than 10 PPM, then repeat the procedure.
For an 8,000 gallon tank, add about 5 quarts, or 1.25 gallons of 5% bleach (50,000 ppm concentration).
Note that laundry bleach is not recommended for potable water as it contains additives.
If you’re working with 10% pool chlorine bleach (which is just sodium hypochlorite and no additional additives) then you would need about 2.5 quarts.
That should work for an 8000 gallon tank in order to kill bacteria if you let it sit 12 hours.
Use a chlorine test kit that can test for high ranges of chlorine residual so you can verify you do have 50 PPM.