Agreed. Looks like a fairly advanced Calcium deficit with the start of a magnesium def showing as well. It's more calcium than mag though. Calcium isn't as mobile as mag so it tends be able to start higher up on the upper leafs. That's where the worst of yours seems to be. The bending of some of the lower leafs say a mag deficit isn't far behind.
That's what I thought.
I have the best tap water in the world economy ec is 0 out the tap
I used to used hesi nutes. After reading the bottle I realised there was no cal or mag in the mix
Changed to ionic soft water nutes 3 days ago
And added 2ml per litre of cal mag aswell
its def calmag and you will be able to rectify it but some damage will be done.
If your starting water is 0ec add calmag until its 0.3ec. then bump nutes up to 1.2-1.4. Ionic is really good nutes and simple and cheap. I swear by them. 0.5ec is very low for flowering plants even in dwc. What power is the COB?
Its definately not light burn. Be pretty hard to burn plants with 200w light. Ive never heard of any plant burning at 0.5ec so it may not have been the nute strength that was the problem.
Leafs were curling down they were very dark aswel. I dropped the ec from 0.8 to 0.3 and they looked loads better within a few weeks
Then a changed light from a 100w mars to budmaster 200w then all this has happened
Hence why am thinking light burn
Plus a have been using hard water nutes when a should have been using soft water nutes
A give them a good dose of pk and cal mag today kept the Base nutes the same
Base nutes was 0.5ec gave them 10ml of pk and 20 mil of cal mag
That put the ec to 0.7