chasv77answered grow question 5 years ago Hmmm, I seem to be following Mrs_Larimar all over and have similar answers😉
Growth issue does not necessarily indicate mineral water issue, unless maybe that water is way way out of the 6.0-7.0 cannabis range, but even then............ I would use distilled or purified drinking water. You could ph it to around 6.0-6.3, but I have never really needed that done.
You may be at risk of over watering, using that plastic pot. I would switch to fabric pot as it culls the roots nicely, drains water through the sides as well as the bottom. You'll never over-water, if you use the two knuckle approach in testing your soil dryness. Should be cool, but not damp.
If your light, temperatures, circulation are good, maybe this girl is just slow naturally. I would not feed at all for at least 30days, if you are using QUALITY soil. IMO, I would not worry about humidity so much, as I grow in a cabinet in dry Colorado air, and my levels are usually around 30-35%. The water saturation of your fabric pots would also help to humidify the air, until bigger plants start to transpire. But follow MRS_L for that dome stuff if it sounds good.
Good Luck.