I'm not an expert grower by any stretch of the imagination, plus I grow outdoors. But I am a practical person, and I say just go back to what worked the first couple of times (the tap water with high Ph). Who cares if it is not technically supposed to be good... apparently it may be good for your plants.

Sorry I can't give any explanation, since I know that is what you're looking for. But if you go back to the regular tap water... let us know how it goes.