Whenever I see those brown spots, it’s always cal/mag deficient. You said you PH to 6.1, I assume you’re growing hydroponically or in coco. If not, that’s your problem. Bump that PH up to 6.5-7 if you’re in soil and it should stop. How much calmag are you using per gal of water? I use tap water also, and thought I didn’t need calmag because tap should have enough Calcium in it, boy was I wrong. Apparently my tap water is cleaner than I gave it credit for. Not everyone’s tap water is the same quality unfortunately.