The message
from "Judanne" contains these words:

I bought a house with a septic which I'd never had before and within a few
weeks of using it, it became rather smelly.

We've had one for the last 18 years (and now have another one at the
new house); no smells and we've never used enzymes. That your new one
quickly developed a smell with use, probably means you put something
down the system that interfered with the natural digestion process. Imho
the best way to take care of septic tanks is to let them work naturally
and be careful what you put down it; only fully digestible material of
organic origin.

What you want to avoid putting down any sinks, drains or lav flushes
is anything that kills bacteria (since they are what work on the
sludge). So, no bleach, disinfectant,harsh detergents, paintbrush
cleaner, oven cleaner etc. If I've used a bucket of disinfectant,
detergent and water to wash a floor, I throw it away outside well away
from waterways; ditto solutions used for soaking paintbrushes. I use
enzyme-free, "non-biological" powder in the washing machine and a
non-bactericide liquid for dishes. Large amounts of oil or grease are
bad for the tank so don't pour old oil down the sink or outside drains,
and wipe out frying or grill pans with paper before washing them.
"Disposable" nappies, pantliners and sanitary towels (the sort with
absorbent granules and plastic backing) and condoms should not go down
the drains either; but pure cotton tampons seem to get digested OK.

HTH

Janet