First Grow

[Takatankata]

Hi AFN,
I joined not too long ago, also hailing in from a recent legalization.
Anyway, I wanted to share my first grow and maybe get some tips, because I think my blooming girl (RQS Cherry Pie auto) is showing early signs of nutrient burn or low PH

3 leaves closest to the light have these small brown patches, and basically all leaves have a bright green to yellow tips. Her water had RQS Easy Bloom booster tablets dissolved in it, but her most recent watering was plain tap water after discovering the little problems.
(the white stuff on the fabric pot is residue of the boosted water, which does worry me a bit)
It hasn't changed much since 2 days ago, but I'd still rather be safe than sorry. I obviously don't want to throw her out a few weeks before harvest.
I have a very bare bones equipment, no way to test the PH of the soil or water.

I'm sure I've made a bunch of newbie mistakes.

TLDR;
Possible nutrient burn, too low PH /Both?
Cherry Pie auto from RQS
Plantop Rosenerde (I've heard that roses and cannabis like similar soil) in a 30L fabric pot.
RQS Bloom booster tablets
Mars Hydro TS600 100W ~30cm from canopy
Shitty old 60x40x200 white closet
Last watering yesterday with ~2L of plain tap water.

 

[Takatankata]

Welp, had to emergency harvest on Sunday night to save the other half of my buds from Budrot. Didn't notice the early signs. A real bummer, having to throw the biggest buds out

Also not that unexpected, as I couldn't get the humidity below 60%. Currently with the 2nd plant in early bloom and the saved buds drying, it sits at a happy 40%.