Just finished a fishless cycle in 4 days!!!! I figured I would share my experience so that others may learn. I am still relatively new to the fish-keeping scene and had only cycled 2 tanks before this but here is how I did it. DAY 1: Set up tank, filled with conditioned water, added plants and decor, put in about 4 pinches of flake food that I had crushed into dust almost to help it break down in the water. DAY 2: Added 60mL of Stress Zyme and about 8-10 handfuls of gravel from one of my other tanks and scattered it along the bottom of my new tank making sure that a large amount was right under the filter intake. I also went ahead and put in the filter cartridge from another filter on another tank that was about a month old behind the cartridges in the new tank's filter so that the water must pass through it before getting to the other cartridges. Added same amount of food again. DAY 3: Checked all chem levels and started to see ammo and nitrites fall, did not do anything but add a little more crushed flake. DAY 4: Checked levels again and ammo and nitrites at 0, nitrates at 5-8 ppm and on the rise. Added 25 more mL of Stress Zyme and planning on adding a fish or 2 tomorrow. This obviously only works if you have access to well used substrate and filter cartridges but it practically cycled my tank over a weekend! I will be adding fish very slowly to make sure I don't get any spikes and monitoring the water closely for the next month or 2 but I think I'm in the clear.