I know this is a silly question but when you're aiming to do a 10-20% PWC
, how do you calculate how much that is? Do you add the capacity of your sump and main tank together and then figure the % from there....or is it better to just go with the % from the main tank?
I'd imagine it'd be better to go with a bigger water change but i don't knwo if it's really necessary. So if i have a 75g tank and an 18g sump...i should be doing between 9-18g PWC
's. What do you guys recommend, lets say for a bi weekly water change...the 9 or 18?