determine the true problem before introducing any additives!
have the laterals been inspected for obstructions? is the distribution box also flooded?
try and examine the laterals for roots or biomat (essentially impermeable sludge that keeps the ground below the laterals from absorbing water)
laterals can be jetted clean of sludge and treated with hydrogen peroxide (industrial; >30%) going forward to help keep them clean
make sure that all of your laterals are being used evenly. if the d-box has shifted over time, one lateral might be taking all the load. "
speed levelers" can quickly/easily fix that.
we had a similar experience a few months after moving into our house. it was root clogs in the laterals. i cut down EVERY tree near our septic field and now add Root-X 1-2 times a year to tank and d-box. no more problems.