However, if you need to set up a tank on short notice or in a emergency (such as for quarantine) these products are a must.
The two products featured below are highly recommended by this forum.
FRESHWATER AQUARIUMS:

The only known product guaranteed to work for freshwater aquariums is Tetra Safe Start.
This product is not to be confused with Tetra Aqua Safe which is a dechlorinator similar to Prime.
You will need both products when setting up a new tank.
Use the ENTIRE bottle of Tetra Safe Start when setting up the tank and add the fish immediately! Pour directly into your filter for best results.
Get it here: http://www.amazon.com/Tetra-77962-SafeS ... safe+start
MARINE AQUARIUMS:

The only known product guaranteed to work for marine aquariums is Bio Spira.
(Instant Ocean brand is the most commonly seen, but it can also be Identified as Dr. Tims Bio Spira)
Again use the ENTIRE bottle of Bio Spira when setting up the tank and add the fish immediately!
Again just as with using Tetra Safe Start you will need to use it with Tetra Aqua Safe or Prime.
Get it here: http://www.amazon.com/Instant-Ocean-779 ... =bio+spira
Please check out the article on Fishless Cycling here: library/water-filtration/fishless-cycling/
Please PM me for corrections or to update this with additional info. Thanks!