It does look like maybe too little nutrients, kinda a nitrogen deficiency, which is strange with such a high nitrogen rating in the NPK ratio.
You can use tap water, overnight out in a wide open container is usually enough, also filling a bucket out of your shower head is good, the misting of the shower head causes most of the chlorine to gas out of the water right then and there. But you could also know what is in your water, at the very least the PH (acidic or alkalinity) and parts per million of dissolved solids in your water, these can be tested with digital pens that can be purchased for around $10 USD online at places like e-bay or amazon.
Miracle grow for tomatoes 18-18-21 would be a better fertilizer for cannabis during most of its lifecycle, and it can be used for the entire grow as well if used in low mixtures. I like miracle grow cactus liquid fertilizer 2-7-7 a week or two or so after the flowering period has started or at least the last couple weeks of flowering, when done right you don’t really need a flush or if you do, only the last couple of days for the flush.
Let’s have you start with a support ticket, answer all the relevant questions and we might be able to get a better idea of what is going on.
ILGM Support Tickett
What is the strain?
Indoor or Outdoor?
Size of space?
Soil or Hydro? Medium used?
Type of nutrients used? NPK? PPM levels?
Vegetative Growth season or Bloom/Flower season? Number “weeks/days” from start of veg growth or into flowering?