I cycled 2 tanks simultaneously. In one I used Cycle with a shrimp, and in the other, just the shrimp alone. To my surprise, the tank without the Cycle completed the cycle in 2 and a half weeks whereas the one with the Cycle did not finish for another 2 weeks. Both tanks are now beautiful FOWLRs, but I feel that the "bacteria in a bottle" products are best left on the shelf. For SW, anyway. Cycle and Stress-Zyme have worked wonderfully in my freshwater tanks, just not the marine tanks.