Only fairly clear water should exist between the scum and sludge layers. Solid material overflowing to leach field should not be occurring. It is this solid carryover which clogs the pores of the leach and causes systems to fail. Two main factors are the cause for solid carry over. Bacteria must be present in the septic tank to digest the solids.
Bacteria are very sensitive to environmental changes.
Many home-care products used in most homes every day will destroy bacteria. Check the labels of the products you normally use. Any label carrying any of the following warnings will kill bacteria. When the bacteria is not present it can not digest and liquefy the scum. The scum will then accumulate until it overflows into the absorption field.