I'm using biomix all mix and ghe Terra aqautica .What medium? If it's not from the earth, it's probably not soil. Either a peat based, compost based or Coco based potting mix.
If peat based, tap water will be fine as it's usually acidic. Has it got any buffering agents like dolomite lime? If you have lock out, and there's salt buildup, 90% of the time it's too acidic, so alkaline water is fine.
I assume it's a peat based mix fed with salts. Have you done a slurry test to verify medium pH?