I know people who test their water once a week but I haven't tested mine in months.. I only ever test my water if I see a problem with my fish. How often do you guys test your water?
On my newly set up tank I tested daily until any signs of a cycle were gone. Now I am on a weekly test schedule. Once I see nitrates I do a water change.
I tested every week for years, until I found the routine that would keep my nitrate level between 2-5ppm, and pH stable from before and after a water change. Once that had been established once per month, or if something appears askew.
I have had tanks running for years that I never tested. In my experience you can do that if you are patient and if you are intentionally under stocking the tank with ample water changes and meticulous maintenance. There are other ways to do it as well. That method works for me because I don't care for the appearance of tanks with what I feel are too many fish.
If I wanted to run a tank at close to maximum however, I would test routinely because it's much easier for things to go south when the stocking is heavy. (Again, from my experience.)
Mostly when I am setting up a new tank lol.I rarely test my established tanks since I am on top of their maintenance pretty much but every now and then I'll run some tests just out of curiosity.
I normally test daily when setting up a tank otherwise about once every month or two unless problems occur, I rarely see problems with my tanks as they all get 50% weekly changes and some get 50% twice a week.