In the beginning I tested often. At least once a week. While cycling it was every day. If I am setting up a new tank I test every day until I feel comfortable that the tank is cycled. Before doing a water change I used to pull out a cup of water. While the tanks were filling I would do the tests. Now? Well, I haven't tested in almost a year. After a while you get a feel for the tank, you know what kind of water change schedule will work for you. I do 75% water changes weekly so I know that I don't have Ammonia, Nitrite, or high Nitrates. Our city water is naturally very hard so I don't need to worry about a pH drop. If something wrong happens to the tank, then I'll test. Plus it helps that in my 55 gal I have True Rummynose Tetras. If the red on their nose starts to lighten, the water quality is suffering. Time to get out the Python and do a change!