hard water does not cause nutrient burn. I have hard water. When you get near 300-500ppm and higher you may need to consider filtering of some sort. Maybe one of those cheap inline hose attachments for RVs / gardening can work? That drops it 50%? it's not a real thorough process. RO will obviously bring it down to 0-5 ppm range.
looks like you got more than one thing going on. Would need to see how it progressed to better diagnose. The red is likely colder temps and/or genetics (autumn colors).
maybe low k? if it paled bottom-up on plant, add some N too. If the canopy is falling apart too fast, definitely try 'something' ... if it's slow-moving and should survive until harvest, that's less of a concern. LEaves power everything - even the stuff you cannot see. If they are all dead, not much is happening.