(John Sankey) Spaketh Thusly:

I presume that by RO you mean reverse-osmosis-purified water.
This is not acidic (except with CO2 dissolved after
purification), it's merely so soft that your plants won't get
most of their essential nutrients. (Unless of course you undo the
purification by adding aquatic fertilisers.) HCl is just as
strong an acid as H2SO4; HNO3 is broken down by biological action
in aquaria as above. All the pH-lower sold locally in fish stores
is dilute H2SO4.
The best thing about HCl is you can buy it in any hardware store as muriatic
acid for about $4/gal. Even with my well water, pH 9+, a gallon lasts me over
a year.

--
Bill H. [my "reply to" address is real]
www.necka.net
Molon Labe!