A lot of people on here use and recommend the API master test kit, they are about $30 at the large chain stores, cheaper on line. The other one I see recommend a fair amount is the Nutfin kits (I believe they are by hagen). Basically you what at a min is ammonia, nitrite, nitrate, pH (high and low, or wide range). If you are keeping or planning to keep live plants you will need additional tests (not sure what they are I don't keep live plants) Other tests you might want for your reference or possible future problems is GH and KH. The other brand that I have heard good things about is Salifert, however, they can not be purchased in a kit, every test is purchased individually, and if you live in the US, they can be hard to find (unless you buy on line) and are quite a bit more expensive then API and Nutrafin. However, if you live in the UK, they are apparently more readily available and about the same price as the other brands. I personally use the API and have never had a problem with them.