Cal/Mag issue or nuteburn? or other?

Hey guys, im growing in 100% coco medium (canna coco bags) everything has been fine with my plants through-out the grow however.
Im now approaching week 5 of flower, and my SOME of my leaves are getting brittle at the tips and a slight amount of curling upward (not canoeing and not from heat/humidity).
I have not flushed my medium in the (3-4 months ive been using it, yes I vegged for longer than 8 weeks due to be an amateur grower I had issues stunting growth in the beginning.
I havnt had much growth the past 2 weeks or so but the problem isn't getting worse rapidly, it just doesn't seem to be going away either.
Feeding Part A+B bloom nutes for coco and +C(Silica based) nutrient, also a few other additives but not any cal/mag uppers specifically and I know that coco lacks calcium.
the rusting on the leaves could be due to that I hand feed and nutrients could spill onto leaves, atleast I know ive burnt some lower growth near roots but I care not for that growth anyway as its 4ft from the canopy.
However I doubt that handfeeding would get nutrient solution onto the middle/upper fan leaves.
Should I flush my medium and see if that does anything or can anybody inform me of the actual underlying issue, as I've been looking all over the internet but its my first grow and ive never had this sort of symptom before.
thanks guys <3

probably worth noting my current PPM is about 1600 the last 4 feedings or so were that high, before that I was leaving it at around 1200-1400PPM without any real issues I just thought id increase to see if my plants liked the higher dose or were happy with the smaller dose (3/5th doses to what the nutrient company suggests).

Water on the leaves allowing the nutes to bleach/burn, or magnify light to burn? It doesn't look random/uniform enough for mg def.

I know the picture was only 1 leaf but out of say a possible 200 fans in my grow tent, theres maybe 20 with this issue.
Given I have 2 oscillating fans in there water could have potentially flew onto it while I was moving my bottle around?
Should I perhaps wait it out?

dopeleader said:

I know the picture was only 1 leaf but out of say a possible 200 fans in my grow tent, theres maybe 20 with this issue.
Given I have 2 oscillating fans in there water could have potentially flew onto it while I was moving my bottle around?
Should I perhaps wait it out?

Click to expand...

Let's c a pic of the whole plant

I'll post one in the morning just did a semi flush as I havnt done one the whole grow cycle, did at 1/4 strength nutrients gave a heavy watering.
Upon closer inspection the lower growth (around where I hand feed the plants) is where this necrosis stuff is.
Im starting to lean more toward just splashes of nutrient solution on the leaves, as my buds are really starting to thicken and that wouldn't happen with such an issue?
Will have a pics up in 6 hours, thanks for replies.