I was actually just telling Mr. Trichome this in the Silica Blast thread- the amount of pH down you'd need to interfere with ferts or salt up the soil is EXTREEEEEEME!
Do not fear pH down, but wear your safety RayBans. Any eye protection is better than nothing. H3PO4 is nasty shit.
You should be fine as long as a) the hardness is not much over 300- you can get 'hard water' nutes for that level and b) you either use buffered ferts and they keep your pH at 6 or you check and adjust the pH frequently. Tap water, particularly after a change to the city water system, isn't as consistent as we would always like to think.