water change question

[Amadod2]

in the past i use to do weekly 10% but was told that wouldn't help the tank because it was too little and too often, . so now i have been doing 30% every three weeks and i been told its too much and the corals won't like that. i want to get into a routine that will not be hard so i can continue to do it and that the corals will thrive over time. i was thinking of doing a 10G water change every two weeks on my 75G as the actual water volume for the tank would be roughly 70G or less so it works about to be a 15% water change. what do you guys think??