I feel you on the rough well and having to filter. I’m in the same boat. With super clean water though it can strip out the goodies or hold them from the plant. I use nectar line and to balance the lack of magnesium & calcium they have a liquid calcium for both. I don’t fully understand it but it works.
I also use plain old epsom salt for foliar but that’s just magnesium. You can water it in and top dress with it too.
My vote is that your water is too clean and if you’ve been really careful with nutes they are actually hungry.
Black mold I’m honestly not sure but I’d think it’d be everywhere and obvious with spores.
Can you snap some new pics with regular daylight spectrum light on (without the hps)?
