Potassium deficiency/underfed??? (pix inside)

So this has been an ongoing issue from veg. Except.. only a few leaves were affected in veg. Now that I'm about 2.5 weeks into Flower I'm starting to see more and more leaves affected by this. One plant is growing in coco and is fed with the same water from the RDWC res. The coco plant is thriving with no issues since the beginning. BUT the coco plant is fairly smaller than the dwc plant.

I've already checked the spots if they are spider mites and they are not. No mites at all on any plants.

Setup:
4x4x7 Tent
600w HPS Ushio Red
2 circulation fans
6" exhaust fan
Dutch Master Gold Flower A + B
DM Gold Add 27 Flower
DM Gold Silica
1tsp Epsom per gallon
EC: 1.9 (PPM @ 0.7 = 1330ppm || PPM @ 0.5 = 950ppm)
pH: 5.7, checked daily (starts at 5.5 and rises to 5.8 before pH down)
Res Temps: 67F on a chiller
Air Temps: 78F at night and 85F during lights on
RO Water, starting at 10ppm (ten)

All pictures are from the same plant, thanks for looking!!










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I would say you answered your own question

yep! you nailed it

Okay, then would I just increase my nute dosage or try to just find a source of Potassium? Thanks again for the re-assurance!

Isn't running 1.9 ec pretty high? Or do I have more room?

thats the problem

awesome pics. i"ve got the same issue starting and because of the "burn" spots im unsure if its deficient, OR a nutrient toxicity.
this thread would be amazing for me right now IF there was a clear answer.
"thats the problem" -what , is the problem?? what are you commenting on? the EC being at 1.9?
FML.
Its too bad we cant complete and cap a few of these threads so that great info isn't so well buried...

anyways, I've got the same problem BUT my number are as follows;
24L distilled h20 @16-21C
ph 5.8
EC .4
intake air 24C
canopy 26C
rh 45-60%
and they are drinking well. maybe 2L/day. while the older leaves are showing the exact same as the plucked leaves in the pics above in pics 3 and 4
bla bla bla.

SO again, should i increase my nutes?
to correct the problem in pics 3 and 4 above posted by aquanaut...

The plant in the pictures is burning up. Your nutrient solution is too high. I would replace the reservoir with ph'd straight water and let them drink for 3 days. Then use a nutrient solution of .7 ( I know it seems low but trust me). They will slowly recover over a couple weeks. In my limited experience when it comes to nutrients less is almost always more! It will take a couple weeks for them to recover. As much as your going to want to do NOT up your EC, wait until your plants tell you they are hungry to feed them more. Increase EC in increments of .2 (better safe than sorry at this point). It will take a while but they can recover.

thanks for the response but you answered aquanauts question from august.
I added nutes this morning anyways and bumped my EC UP to .5 and nothing has progressed as far as getting worse goes.