do i really need to do once a week water changes cause ive upgraded my filter to a fluval 405 its for up to 200 gallons and i have a 70. How often would you guys do them I have a 4-5 inch tiger oscar,2-3 inch convict cichlid, 5-6 inch severum cichlid, 1 blue gourami,1 opaline gourami, 2 serpae tetras, and one swordtail, a pleco,1 red claw crab and a snail.