So I’ve often always wondered this next question so here we go, do you calculate your water changes by the total water volume in the tank/sump or do you calculate it by the total gallons of the tank? I have a Biocube 32g and with rocks/ sand it holds roughly 23 gallons of total water volume. Whenever I do water changes I just change 3 gallons at a time once a week, am I doing this correctly?