Flushing soil... 1st grow ever... am I doin this right?

Plant's about a month old or so... Was real cold till recently, to the point it kinda made it droop and shrivel I guess, still had good color and looked healthy... anyways, stuck a heater in there and it perked right up, but the leaves have a brown kinda burnt look on the verrrrrrrrrrrry tips with a couple similar spots midleaf but only on the bottom 2 leaves. From what I read, it's too much nutrient? I've been feeding with tap water (recently switched to distilled) and an eyeballed amount of Fox Farm grow big (I now have a measuring cup). Pretty sure it was heavy on the eyeballing now.

So anyways, I decided to flush with sledgehammer, just mix as directed with big bloom and drown the thing with 2 gallons? or what?

If so, how long till next feed... It's gona need some time to air out right?

it sounds to me that you may have a magnesium deficiency. you mentioned that you started using distilled water witch contains no calcium or magnesium. i would say the first thing you try is adding a cal/mag supplement to go with your normal feeding regimen, or a very lightly toned down feeding regimen if you feel like you are over feeding.