I just finished cycling my 100 gallon aquarium in a week and didnt even use fish. I have a 1000 gallon pond out front and I use Microbe-Lift PL during spring and summer, its amazing stuff, (bacteria by the way) It keeps the water crystal clear and the inhabitants of the pond healthy. So, I got to thinking why couldnt I use this to cycle an indoor aquarium, same principle really. I had to do some calculations cause the directions are for large ponds but went on the safe side and only added a small ammount, and also, a few flakes of fish food (for ammonia). the next day BOOM the cycle was in progress, I already had a lot of ammonia, some nitrite and a tiny nitrate, well over the next 5 or six days it cycled itself completelly, now its been about two weeks, I have 20 sebra danios in there and there doing fantastic, I think im gonna use this on all my tanks now