The way I see it,after trying both routes (water changes every month and going 6 months without it)I f you like your corals to grow and florish you should have a regulated water changes to simply replenish the ions removed by the inhabitants (not only your Calcium,magnesium,alkalinity)
Every situation is different as in mine I do water changes every 3 months or so simply because entire water volume in my system at the moment is over 400glns and only medium load in a 180glns display and if you know your tank and its inhabitants well some of your corals will let you know when to do a water change as in my system my neon finger leather lets me know same as some of my SPS.My 2c
