Issue with my seedlings, any idea?

[bob_ross]

This is my first time growing. I am growing in a coco with perlite. I buffered the coco beforehand with calmag following cocoforcannabis. It seems my seedling is struggling. I am in colder climate so its little bit dry here. My RH went down from 60% -> 40%. I tried dome but i was getting water spots on the leaves. I put it back on today. It looks like one of the round leaves is halfway dead. Any suggestions?

 

[imakandi]

coco is a little dry
keep moist
with low ec
and wait, it will good
if dome, then holes in dome for air

 

[Dropped Cat]

Seedling heating mat, thermostat controlled.

Although I veg and flower in coco, all my seeds are popped
in organic seedling mix. I do that because my strike rate
with seeds in coco was less than 60%.

In soil, 99%.

When I up pot, the well rooted seedlings get rinsed of the soil
before placing in the coco pots, some soil residue, but minimal.

Coco and seeds not my friend.