Your leaves look like they are "praying" for water. Your soil also looks extremely dry.. 700ml? how big are the pots they are in? if its anything > 1 gallon 700 ml is way too low. You should immediately foliar feed them with distilled water ph adjusted to 6.5. And an oscillating fan should be running pretty much all the time. Think about the outdoors, plants need constant circulating air to strengthen the stems, remove toxins from the leaves, and promote nutrient uptake. I would recommend at least a 1/4 gallon flush of plain water, constant air circulation folair feeding, and get a humidifier for $30 at a conviencie store, and a humidity monitor. Generally anything below 30% is extremely dangerous. 40-70% should be your general goal. A 600 Watt HPS will suck the moisture out of air like the fires of hell. I destroyed 6 crops when I first started growing because my 600 watt was simulating the surface of venus LOL. Good luck man don't give up.