pH adjusting chemicals in general do NOT work. Hard water generally have high KH
(or buffering capacity), so it will resist pH changes. Using any pH adjuster will simply cause pH to bounce up & down ... which is much worse than an out of range pH.
Depends on what your water is like, it is generally NOT necessary to mess with your water chemistry. Within reason, most fish will adapt to an out of range pH. The only reason to mess with the water is if you have some exotic species or if you are trying to breed discus & the like.
To alter water pH effectively (and to maintain stability), you need to change the buffering system. This is more complicated than just dumping in a bunch of chemicals. Your best bet (if you really want to doctor the water) is to mix in R/O water & tap <or R/O & salt mix if you are doing SW