Even though the old school aquarium rule of thumb was to perform 20% water changes every two weeks, there’s really no right or wrong amount or frequency to abide by. You could do 100% water changes every single day if you had the time or financial ability to do so. Unfortunately, this requires a great deal of effort and some hobbyists even get away with rarely (or even never) performing water changes. Of course we don’t support this kind of laid back behavior, and we recommend that you find what’s most suitable for your aquarium system. Smaller tanks benefit from small but frequent water changes, often on the scale of a couple of gallons per day. Larger systems are more stable, but would also benefit from regular small water changes. The goal to the entire process is to remove excess nutrients from your saltwater, while at the same time replenishing the beneficial elements such as calcium and magnesium. Try different water change frequencies and amounts, see what your livestock responds best to, and execute that plan with regularity.