Im doing my f/c right now. 50 gallons of water. 5ml of 10% ammonia (ace hardware janitorial strength ammonia) equals 2ppm ammonia. What size is your tank? Start out with 1ml per 10 gallons and then test a hour later just to fine tune your measurements. My tank is 55painted gallons but you need to subtract for the space substrate takes up, and then try to figure in the water in your canister filter( if thats what you are using).