If that is just silica sand, then not really, for pH anyway. Might help with bioload though.
Calcium carbonate based substrate, such as crushed coral, would help more directly with pH.
About the vinegar... "cleaning" vinegar is stronger and might give faster results. And, vinegar powder can be even stronger, if you mix it with little water.
Sorry for the delay; did not see the emails.
Depending on the year and what I'm testing, I'll keep various thing. Been more SW that FW but am wanting more FW.
I'm fishless currently since moving to UT.
Yes that's one of the reasons for coming here. Have not used local water though; I now use only distilled for everything. I think the local reef club probably uses RODI mostly too. Not sure of the local FW folks though.