A properly designed septic tanks and drain field really doesn't need additives. From what I understand, some of the tank additives can actually cause more trouble than what they claim to help. If too much of the waste is "digested" it will overflow and eventually adversely affect the drain field.
IMHO, the key to a septic tank is to keep everything out of it, except for what it was designed to contain. That includes lots of beach, antibacterial stuff, presription meds, water from cleaning paint brushes, oil & grease, hand wipes & female sanitary products, etc & etc.
If you feel you must add something, do as one of my neighbors does. Mixes one package of instant yeast with warm water, per month. Pours down the kitchen sink. Sends it to the tank with more barely warm (too hot will kill the yeast).
Can't remember now, how long he's lived there. Been quite a few years and the tank hasn't been pumped. BTW, we've lived here since 1974 and have had ours pumped one time. Never used any kind of additive. Just try to keep out as much as we can of what shouldn't be in it.
We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.