Simple analytical method for determining chlorine requirement
Take four vials of the well water.
Inject a diluted bleach solution to simulate injections of 0.5/0.7/0.9/1.0 mg chlorine per litre.
Measure the free chlorine residual (and if possible total) after 1/2 an hour or the contact time actually applied in your tank.
The residual concentration closest to 0.5 mg/L will give you the appropriate rate to apply.
If you cannot titrate the exact concentration of bleach (degraded concentration over time), perform a parallel test with distilled water and take the measured value as the injection rate.