With the purchase of any livestock order over $20. Just put in the notes what test kit you would prefer, please list 3 and we will fill them based on availability at the time of shipping. You can choose from: Nitrate Test Kit Ammonia Test Kit Phosphate Test Kit High Range pH Test Kit Calcium Test Kit Box KH Test Kit (Carbonate Hardness) Copper Test Kit Box All of these are API test kits. ONE CATCH - Cannot be used with another discount, and cannot be used with rock because it has to ship separately. That is technically two catches, but I said "on any livestock" order, what I really meant was any order other then rock orders, so in reality I am freeing up the original limitation a bit, so that isn't technically a catch. It is in the rule book, you can check it out here. I will post here when I think we are out of all of them.