Hey @milkmann welcome to AFN and thanks for checking out my grow. Your set up sounds good man... hopefully I can help sort out what the problem might be.
My temps / humidity vary a bit depending on the time of year, like for my current grow my humidity has only been 20-30% and temps around 22-25°C. I don't run a humidifier and honestly have never been concerned with low humidity as it's never been a problem. With LED's you can run around 30% humidity for entire grow cycle just fine, you can also run higher temps than normal and actually temps of 28-30 are ideal for LEDs. So your current temps and humidity are pretty much perfect now so don't think that's your problem imo.
As for my initial feedings/watering... had to look back at what I did for this grow because honesty I just wing it a bit each grow So, for this one I did...
So you can see when I did the first feed with 1.5L each I didn't do another good watering until 9 days after that with just a small watering in between (probably 200-300ml). So the medium was definitely getting pretty dry with that much time between... I'm a bit curious as to why you think your over-watering yours? (what symptoms are you seeing?) Firsty, coco is a very forgiving medium and almost impossible to really over-water. Also if you've just been giving them 100ml or less into a 15L pot that should certainly not cause any over-watering symptoms, seems more like that would be under-watering. What nutes are you using and what have you been feeding so far? Could be you haven't been giving them enough nutrients... Coco has nothing in it so they need some N right from the start. You can see I add cal/mag supplement to every watering (including initial pre-planting watering) which has a bit of N in it, and I start feeding grow nutes by day 5.
Thanks for the reply. I've had a frustrating time on forums recently getting any good replies from people and it's been making me panic about my seedlings, so it's much appreciated. Interesting information regarding the temperature and humidity. I'll be sure to reduce the mister frequency as low RH certainly worked for yours!
I'm watering when the medium is dry in inch down, usually 3-5 days after watering. I was using a syringe to measure out 40ml at the beginning and water in a small circle around the plant, which is why I was so intrigued/worried by my own technique of your 1.5L water for such young girls! I started them on Canna start (all ph'd within coco range) and have recently switched to 1/8 strength GH trio with cal/mag @ 1ml/L and some root protector. I have attached a picture of the seedling in it's current state. The other two seem to be okay, this is the worse one and it just isn't getting any better 5 days after the last watering. The girls are 12 days old. Apologies for the rotation, not sure why it's changed it to that!
Any help or advice would be appreciated. Thanks so much for the info so far!