Hard Tap water Coco DTW

So I've taken a look at both of your diaries and here's what I'm thinking. You seem to struggle with calcium deficiencies, yes? You're worried (in this question) about a pH of 7.5 but your diaries suggest you've been able to tame that getting it down to 5.9... This SHOULD be enough to avoid a calcium deficiency but the other cause of that deficiency is nitrogen toxicity... too much nitrogen will cause a lockout of calcium... So here's what I'm going to suggest to avoid crispy/burnt like hell leaves... when your plants go into pre-flower, cut back by half on the Canna A (I know, I know, they tell you to use it throughout the grow but don't)... and then when they're in flower, cut it out altogether or at LEAST reduce it to 1/4 strength... the Top Max and Bio Heaven you've used in your current grow has small amounts of nitrogen and SHOULD be enough for the flowering stage - which doesn't need much nitrogen at all! So basically, I don't think your problems have anything to do with your water... as long as you keep the pH where you have it, it should be just fine... but I'd take a hard look at Canna A... I think THAT is the culprit here... Good luck!