My lfs sells this. I've been wondering about it too. I have a new 55 gallong set up (EVERYTHING including hood enclosure and stand) on layaway. Was wondering if this would be the way to cycle the new tank quicker.
I have cycled 6 tanks using Bio-Spira, ranging from a 3 gallon to a 20 gallon. Each has cycled very quickly (though not instantly), and in each case the levels of ammonia and nitrite never got high enough to do any damage to my fish. I posted a summary of these cycles here: http/www.fishforums.net/index.php?showto...655&hl=biospira
I've had the exact same experience as krash. I will never cycle another tank without it again. As for cost, it runs $10 around here for a pouch that cycles up to 30-gallons. Only the actual fish store around here has it... none of the chain stores do. I have 10-gal tanks, and 1 was going through a mini-cycle at the same time I set another up, so I put about 3/4 in the new tank, and 1/4 in the old tank. It did a great job!