I have a 180 gal. marine tank with a 30 gal. sump... I do 20 gal. water changes a week, is this to much or to little. I fine it uses a lot of salt, (tropic marin pro) this way. My question is..... do I need to do water changes that often or can it be done another way if so please enlighten me on a more efficient way of doing water changes. Thanks everybody... a lesson to be learned signed newbie