Border Beater - Lemon Haze

Things weren't getting any better treating for nutrient burn. After 10 days of just pH balanced water, new growth started showing yellow tips and a couple of days ago, brown spots on one leaf that was clean before. SO - I've done some research and come to the conclusion that this is likely to be a Potassium deficiency - which would make sense as it got worse after I stopped giving nutrients. Why a K deficiency when I'd been using a good organic NPK ? Well apparently it is difficult for the roots to absorb K if the pH is higher than 5.5 ish. I'm in a hard water area and the tap water has a lot of calcium. Base pH for me is 8.5 @ 299 TDS. I was getting the feed down to 6.5, consistent with the coco substrate. Now I've spent 2 days fergitating with a NPK and some trace element boost. TDS is 892 @ pH 5.56 I don't know , could also be light stress I suppose. We shall see.