i was wondering if the black stuff at the bottom of my undergravel filter would help cycle my 125g, also if i used old aquarium water from my 55 and 40, if i runned 2 matured emperor 400s if it will make my tank fish ready within 2-3 weeks of set up.
The water will not help you cause there is no biological bacteria in the water column. The cycled filters and the dirt from the other cycled tanks will help. But once you get this going you need to feed the seed bacteria with some clear ammonia from your local grocery store. I do not see a reason why you could not have this tank cycled in this manner in 3 weeks. Read up on fishless cycling for ammonia dosages but I beleive its like 5-6 drops per 5 gallons. You will also need a test kit to measure the parameters and to find out when it is cycled. This is by far the best way and humane and the quickest. Some people say to throw some market shrimp in your tank and let them rot in which gives off ammonia But no thanks.