Compared to muriatic acid your starsan if diluted is a very weak acid. Any etching it might be doing is taking place on a very microscopic level but Im sure over the course of several years you might notice the surface getting a little rougher. Its not something thats going to eat your tubs though.
If youre rinsing it off right away your 'damage' is going to be even less because there is really reduced contact time which acid needs to react with the basic nature of the concrete.
To be extra safe you could spray it down with a solution of baking soda and water at a rate of 1/2lb baking soda to 5 gallons of water which is the standard for neutralizing a 10:1 mix of muriatic acid after etching a floor/drive/garage.
Keg2: Gnome Cream Soda
Keg3: Edworts Apfelwein
Keg4: BM's Centenial Blonde
Keg5: BM's Tits Up IIPA