thats an interesting bottle/holder combination. Can you show us more about it?

Why? Finding bottles that fit 3in net pots is not difficult and the downsides of this are just not worth it.

Oh, are they not in net pots? If there is not a space for air in the root system it could lead to rot and stagnant air

Ah, Ya, I dont know a lot about polyurethane toxicity, just seems like a diversion.
I’m eager to see your results.

Yes, white and furry is ideal.
If they turn brown or get sludgy you have a problem.
Air can darken them, so older roots will darken over time.

Socks! Brilliant!

http://my.windowfarms.com/
this will help you find plants to use

But ya, it could also be cold damage…

it looks like it could be a root problem. Dial back your water schedule in the cooler months, more frequent in the summer. But I have seen similar issues with overwatering, roots drown or become anaerobic and bad things happen, are your roots white and furry?

clear image would be better

or you can use Peat moss or coo coir in egg cartons.

I dunno if I’d wanna be eating polyurethane, those roots will deffo consume it.
I use potting soil in egg cartons, it’s not the best option, but it is basically free.
I also use rockwool or compost plugs for the more cherished varieties.

Go here and enter your info
http://my.windowfarms.com/
from there you can get recommendations on plants that will work for your situation.
Sounds like a Partial Sunlight situation and I would recommend about 25watts of fluorescent, if you are inclined to augment the lighting. Otherwise, just use low light/partial shade varieties.

There are several things I need you to share to delve a little deeper. –Firstly, I can’t really see the image of the strawbs, but if the crown is too low, they will rot. –Secondly, it looks like you are using a chemical fertilizer. Have you been pH balancing your solution? The NPK looks fine, [...]

I get the very same air back flow issue you speak of. I have been able to resolve it by maintaining water levels and adjusting the t-joint to the right level in relation to the reservoir.