Humidity low

Your soil mix is too "hot" and this is what is burning your leaves, so no need for nutrients for another 3 weeks or so. Humidity is not the issue or a problem. Growing at 24/0 IS a problem though, go to a much more plant friendly and healthy 18/6.

Its not your humididty. I have germinated a seed and it had no issue in RH 25%. If your leaves are curling then your most likely feeding them to put. Or the soil you put them in has to many nutrients in it. Its hard to tell without knowing What your growing in? What your feeding and how much? Do you adjust the PH of the water your using?

After looking at your diary. Your issue is you are over feeding. Hard to see in purple light. You have nute burn. Which has also got your ph likely really low. Especially if you did not have run off when applying nutrition. Your nutrition amount and when is off. In soil it is feed. Water water feed in wet to dry cycles. If in coco your feed schedule is different.

To be honest, your humidity is fine except if you had seedlings in the tent. To increase humidity, if you feel you need to, all you really have to do is to hang some wet towels from the top cross bars - hang enough of them until you get to the humidity you think is right. Personally, once they leave the seedling stage, all my plants are in a humidity of about 40-50% but when they get to flower, I try to reduce that to 30-40%. I think one of the problems you're having has everything to do with your pH, not humidity. Growing in soil, you need to maintain a minimum pH of 6.0. 6.2 is ideal but it can go up to 6.5 and still be ok unless you're in flower when 6.2 is where you definitely want to be. A pH of 5.8 is not allowing the plant to access the nutes (which you say you are giving but do not report on in your diary). Bring up that pH, you'll have a much happier and healthier plant. Good luck...