Fresh, cultured bacterial solutions can fast start a tank. The key word is fresh.
...The word "instant" as used on some advertising isn't accurate, by the way.
My specific problem with most products that are advertised as living bacteria culture is the date, or lack of a date, on the bottle. Bacteria are alive and stay that way by feeding and reproducing. You can slow the culture down, but if living things don't feed, they generally perish.
What you'll find at most stores is a dusty bottle.
If you can find a great fish shop that sells living cultures - that they use on their new tanks - great!
