Light Stress or Light Leak?

I got the same problem in rdwc. Every winter even its 18celcius at coldest during night. I think its cold problems

That’s either still the light stress or not enough Oxygen to the roots. I have seen a friend grow in a Nft with no cover so the roots were totally exposed and they did not droop like that. Back the light off even more until they recover and check air pump and air stones to make sure there is sufficient aeration. Also too hot or too cold temps will do the same thing, normally it’s the hot temps that affect them the worst. Hope this helps trouble shoot buddy👍

Could be light leak on the roots, cold temps, or pH/EC is way off. Home Depot buckets are also NOT food grade, so that may cause you some trouble. Not sure how the polys could react with the plants and your feed.