My tap water pH is 7.6, so I always have to add lactic acid or citric acid, even with gypsum and CaCl addidtions. I don't brew a lot of stouts(any stouts) so on those I might not need acid....
My water is ok for brewing. I have on my to do list to update my water report with Ward's Lab. It's been a while.
The more reading you do(to a point, I find I get glassy eyed after awhile) and video study you do the better(I've said it before, there are some good you tube videos on applied water brewing chemistry,more helpful to me).
Of course there is no substitute for actual brewing water treatment, the more you do, the more comfortable you will become, and your brews will improve.