HELP! Plants appear to be dying

[Demonickus]

Someone please help i am first time grower and i have 2 problems actually. first is my babies i started from seeds, they are growing really slow. they are in a grow room i constructed and lined with aluminum foil. they are in jiffy seed starting mix potting soil, led lighting 18 on 6 off, i water them twice a week. i have a digital heater set to 78 degrees. (see pics). My babies are 8 weeks old. and they are barely out of seedling stage

my second problem is a plant i was given that was in trouble. it has just started the flowering stage, but it was starting to die, it is on led lighting 12 on 12 off. i water it twice a week. i have given it nutrients for nitrogen def, but nothing seems to be helping. i have had the big plant for about 4 weeks and the level of flower growth has not increased. the decay in the pics was like that when i got it but it seems to be getting worse. is there anything i can do?

[SoOrbudgal]

It appears that big plant is rotting or is in revegg mode? I would hope it's not a bug issue but it could be and you could be overwatering if you don't let those plastic pots dry and no holes. Does it sit on cold service in water? Those peat pots are OK but won't break down fast in what you got them in roots suffer. I use plastic pots but only with lots of holes drilled in for drainage, good soil with perlite stones for air mixed in.

[Canuck147]

Sorry but your grow medium looks like crap - no perlite - ugly mulch? Your plants aren't going to grow in that - my opinion.

Your plants aren't growing well cuz your roots are underdeveloped - can't aerate can't get any oxygen and yes your roots need oxygen - that's why one let's their pots dry right out - let's the roots catch some air.

Happy roots will lead to big buds.

[kingfish]

I would scrap the whole lot and start over. But before you do, read this. Intro: Learn How to Grow Weed Indoors

[PLreef]

Your soil looks more like mulch than actual potting soil. Adding perlite helps the water drain and your roots can breath. They look like they are suffocating. Maybe over watered??
What kind of lights are you running and how high are they? Remember light = food.

[Rwise]

I too see reveging on the bigun, once a plant reveges the flowers will die off and MUST be removed or the dead will cause mold problems (hint get all that dead off her). She should be right on top of flowering at this point, she should have made the change back to flowering, unless you have a light leak.
Have you done a bug check?
What is the PH?
Need input!.

[Rwise]

And the we can talk about light penetration into the plant and even canopies.