The recommended levels in the pool math app are based on TFP guidelines for the type of pool surface you have be it vinyl, plaster or fiberglass.
The generic levels recommended by Hayward don't recognized the interaction between CYA (stabilizer) and chlorine (FC). Nor do those levels take into account the different needs of different pool surfaces in terms of proper water chemistry.
The Pool School link up above is a great place to learn what we are all about here at Trouble Free Pool. Our methods are based on solid science and backed by thousands of independent results from pool owners such as yourself. The best part of it all is leaning from us won't cost you a dime.