I do not think where you live has poor Ca and Mg, unless you use RO for all water changes, it's highly unlikely.
I get sierra snow melt, about as pure as water gets from the tap(they sell it for bottled water), I do not dose that much GH.
If you limit ferts also, well, like a bonsai, the growth will be stunted, this is not reduced internodal length, this is a stunted plants, this is a rather large difference. You can limit several different nutrients and have this occur.
Keeping to teetering between stunting and the desired spacing is a PITA and fruitless over the long term realistically. Some manage to do it for awhile, but often had issues over time. Being a green thumb should not have to be such a headache I believe and advise.