EC of 1.9 seems quite high to me, especially if they have already finished their stretching (usually during bloom you go down with the amount of feeding). Since you're in DWC, that should be quite easy to measure though (that's what i like about it.).
What was the EC that you put in? What's the DC after a day? Did it go up? If so you're overfeeding (or there is a lot of evaporation).
If it goes down, you should be feeding more.. if it stays the same, it's good.
Measuring EC is the only way to know what works for YOUR environment. Following what the manufacturer say, is like following a dog-food manufacturers advice of 'give one can daily to your dog' without knowing whether you own a chihuaha or a rottweiler. ;)
In my bonsai grow, if i go higher than 1.4 i get lightly burnt tips, so i know i have to stay below, but that's only under a 50W COB (wall drawn 50 watts.. not marketing 50 watts), and that was also during vegging.
Did you measure the PH? In the past i had similar behavior (on my chili plants) when i didn't measure PH and EC daily, and didn't adjust it accordingly. I had PH drift, didn't catch it and then the plant couldn't uptake the nutrients correctly.
DWC is in my opinion quite easy, but it requires a lot of measuring of EC and PH to ensure they stay happy.. i do it at least once a day.