RQS Northern Light - Leaves

When I read "Hessi grow 4ml per 1L," that's what you give to big plants, mature ones, not seedlings. Be glad it's still alive. Stop feeding it immediately, just water for the next week with cal/mag, nothing else. Then you can try 2ml per L, but only in about 2 weeks.

change reservour and add only cal/mag till EC 0.5

looks like a iron deficiency...check PH but iron deficiency can also occur due to overfeeding(lockout), the deep green color of the seedling looks overfed so best check EC too (in this stage you mostly only need 0.4-0.5EC with calmag only, no or almost no fertilizer

Sorry for not adding my diary, I am new here. Here are my measurements from last days: On day 3 I added nutrients: 1ml/L Hesi Growth, 1ml/L Hesi Complex Till day 10: ph around 5.8; EC(ms/cm): around 0.20; I was fighting with water temperature which were 24C. On day 10 I cleaned my reservoir and added nutrients: 4ml/L Hesi Growth, 1ml/L Hesi Complex, 1ml/L Hesi Zyme. After 10th day I was fighting with ph from 5.3-6.2; EC(ms/cm): 0.62; water temperature are also around 24. Light was position on 60cm from plants, and the light is TS1000. Hope, now I give you more information for better help. Thank you all!

I'd love to help you, mate... but you haven't got a diary so no one can see what you've done/not done, can't see what your conditions are, what nutes (if any) you giving... you need to give us more information if we're going to have any chance of advising you with any degree of certainty!