Hello Elias2107!
Glad to see that you're growing! Is this your first grow or have you been growing a while?
Taking a look at your pics and reading your post, it looks like your little seedlings are suffering from what many new growers to - giving their plants too much love!
When cannabis plants are seedlings, they're very tender and fragile (I've never had a kid, but I imagine that's what babies are like?) and while they are resilient thanks to evolution, they can suffer from too much attention and care.
Seedlings are extremely special in that they initially have all the food and nutrients that they need to get started so no nutrients are needed. So if you're giving them any nutrients, that can probably stop for now. They're also sensitive to chemicals so if you're adding any pH-up or -down, you might want to cut back on that as well.
It also looks like your rapid rooters are extremely wet. While water is essential to plant growth, when they are seedlings, their roots don't really have the capability of absorbing much of it. When they first pop, seedlings actually take in more water from their leaves than their roots. If you're thinking, "Gee, maybe that's why seedlings like higher humidity than adult plants?" you're absolutely correct! Also, when seedlings are overwatered, it actually suffocates the roots causing all sorts of problems. Roots need oxygen/air as much as they need water.
Your little seedlings are looking pretty rough, but by going a little more 'hands off' you might be able to salvage them. My suggestions:
- Stop adding nutrients for now until they're bigger
- Stop watering for at least a few days.
- When you do start watering, give them VERY LITTLE (when my seedlings are that big, they just get misted using a sprayer. Once they're growing strong, I start doing about 1 cup (about 250mL) every 2-3 days)
- Also when you water little babies like that, try watering in a circle an inch or two (3-6cm) away from the base of the stem. This helps keep the medium wet without drowning the developing roots.​
- And in general, you want your temps to be between 68-77F and humidity 65%-70% during the seedling phase. However, it appears that the watering issue is more prevalent than your environment at the moment.
Good luck, keep us posted, and remember that (usually) less is more with cannabis!