Further thinking, this is really the same problem on every grow when I look at my journals.
Start the grow, everything is ok.
Flowering phase begins, plants look healthy, minimal feeding.
Plants start to look hungry, begin feeding flowering nutes at 1/4 strength.
Tips start to go yellow/brown - looks like nute burn, really?! I've hardly been feeding them
Ok, back off the nutes then I guess if I'm seeing nute burn.........then things get worse
What happens then is that I just end trying to nurse plants through to the end
Same light, same soil, same water, pH around 6.5. Now my water i think is on the hard side, I have a water softener but I don't give this water to the plants, I use the non-softened tap. So I'm thinking that maybe there is an excess of calcium in my water which is locking out K and Mg - that's another thing, I always get a mag deficiency.
I have measured the EC of my tap water and it comes in at 0.3 - 0.4, which I believe is not bad? Maybe someone has more of an idea about that or whether that's an indication of how much calcium is in my water....