Can't remember where I read it, but I remember reading something that stated a 1:10 dilution of bleach was more effective than using bleach straight!
Several other things to consider:
1) In chemistry lab, one is taught that you should always add the concentrated chemical (bleach) to the water, not the water to the bleach. This is for safety.
2) You should not have to be spraying after every shower for mildew. If you really want to, check this article: http://www.food … y-cleaner-349641
3) OSHA does not recommend bleach for porous surfaces. The mildew comes back because its "roots" are deep in the grout and not killed by the bleach on the surface.
4) another recipe some people suggest is using rubbing alcohol in the sprayer.
5) Bleach is a base, and they are corrosive by nature, especially concentrated. Grout and tub surfaces can be damaged with daily use.