I have a 500 gal stand alone spa and been using Leisure Time Spa-56 (Sodium Dichloro-S-Triazinetrione Dihydrate -99%). Does this chlorine type add CYA? It seems over time, after replacing the water, I need to add more and more chlorine to the water leaving me to suspect the water is accumulating too much CYA. And by the way, the spa dealer tells me not to worry about water hardness for Spa's especially if I get water from the city. Thanks.