Water changes are the same as with FW tanks with water needing to be changed acording to bioload, on my 80g brackish i only change water once every 3 weeks as the protein skimmer and nitrate adsorbing media take care of the water quallity for the main part and on my 20g brackish i change water every 2 weeks as it has a very low bioload with just 6 bumble bee gobies, a 2" GSP , 2 sand gobies and a flounder in it.