" Bubble" | First grow !

In soil you can grow between 6 a d 7ph so 6.5 is the middle value , but a brutal switch can stress the plant. Forget about the boron deficiency except if you are re using a old soil it's a pretty rare early deficiency. Mineral water have ... mineral in it like Calcium Magnesium and others stuffs RO water is pure water so you will have to add cal mag and others micro nutrients to compensate so do you really wanna do that ? My guess is that you over watered your plant , the soil does not looks dry at all but the opposite ( not really the opposite but more moisture than what you should )