IF you use the hot tub during the day or have it uncovered for any reason during the day I would put in CYA. The most commen form of chlorine for hot tubs is dichlor. This is what is usually recommened by hot tub dealers when you go on a chlorine system. Dichlor is stabilized chlorine so it will add cya to the water. My hot tub is chlorinated by my SWG and has a CYA level of 70 ppm. If you maintain a steady FC level in the tub like you do in your pool there should be no problems! It's when people ignore the tub and only chlorinate it when they use it that it becomes a bacterial stew!