i have a crappy test kit and cant afford the good ones lol so i really only test my ph and my nitrates but I have figured my tank out some so i see signs if anything is wrong
In the beginning I only did it whenever I thought I needed to, and just the basic tests. Then there was the every-so-often period as the tank started to mature. Recently Ive collected pretty much every test kit I want to have and have been testing everything fairly often. Especially alk and ca on a daily basis, along with the trusty Pinpoint pH monitor. I'm due to get my new Myreefcreations calcium reactor any day now so Ive been making sure all parameters are where i want them before it gets installed.
My system is over two years old and currently I test calcium/alkalinity about every 2-3 weeks. There is seldom any fluctuations in levels. Ph is tested weekly...no other tests are run unless a problem developes.
Testing on a newly established system would be much different...with more regular testing of ammonia/nitrite/nitrate.