Tetra Safe Start is supposedly the unrefrigeratored version of the old Biospira. I have used it once, successfully. Dr. Tim's is a different product created by the original inventor of Bio Spira. I have also used it successfully multiple times. (Although once it did not work. That time I"d ordered it online and I wonder if temperature variations damaged it.) I prefer Dr. Tim's although I can't say exactly why. I have dumped Dr. Tim's in a tank undergoing a mini cycle (.5 nitrite) and had it remedy the situation overnight. When setting up a new tank, I also used it in addition to using an old filter for "instant" cycle.