HI,
I think you said you were using bottled mineral water as your tap water was high in sodium? I'd keep on with the bottled water, I used bottled mineral water for many years as ours is very chalky here. Lemon juice is common to lower PH (acidity), just literally a drop or two. Main thing is to not overwater and not to feed at all yet, just let nature take its course and let the plant put down some roots. You want a PH test kit that measures between 6.0 and 7.0, its normally just a couple of drops that you add to a 2ml sample from your water and compare to a colour chart, they are very cheap but do fine. PH is not so crucual in soil to be honest, thats why I think its a watering issue, you need to make sure the waters reaching the roots so stick your finger down a couple of inches!
Good luck.