question/problem with rockwool cubes

i am growing two plants and it seems like one plant is dying. the rockwool cube turned a very dark green in the dying plant and the plant that is healthy's cube is normal. what is the cause?does his mean something?

Mold/mildew? Keeping it too moist? Does it smell funky?

How is the dying plant's stem ? is it soft, or normal ?

its soft and browning. it doesnt smell weird, but if i touch it, it leaves green color on my hand.

Sounds like algae or fungus, does the light hit the moist rockwool?

Hm, It might be stem rotting. try to use less water in the rockwool cubes

ok, ill try that. yes, the light hits it well.

Try to get all the access moisture out of the rockwool. Keep it moist but not too wet. Cover the rockwool from the light. I use use black plastic garbage bags, cut to cover it to avoid that algae.

wet rockwool + light = algae