i keep mine between 75 and 78 if it gets to high i bought some inexpesive ice packs keep them in the frezzer and thorw them in the sump resivor till it come down dont have the money for a chiller right now
70, IMO, is downright cold.
78-84, though most people stay on the lower end, is reasonable in my opinion...though it partly depends on the animals you are keeping. Some (e.g. Catalina gobies) do prefer cooler water systems.