At Least 75 Feet
According to the Florida Department of Health, a septic tank should be located at least 75 feet from your well.
Find Local Requirements
Every jurisdiction has its own requirements, so check your local building codes and health department for the requirements applicable to your location. In addition to distance from a well, there may be requirements about how close the tank can be to a body of water or drain field requirements that must be met.
The septic tank should be as far away from your well as possible, but it must be least as far away from the well as required by local building codes and health department regulations.