Pictures would really be helpful here. It's pretty hard trying to understand your problems without seeing it.
For one thing, big rockwool cubes running in an ebb & flow system is a very fundamentally flawed approach.
I noticed you mentioned you haven't watered because the rw is staying wet for days.
You also said they were the six inch cubes, but you also mentioned hydroton dust, so I take it that they're sitting on or in a bed of hydroton in the e&f tray ?
Big cubes of rockwool just weren't designed for e&f hydro...
They were designed to be sitting on rw slabs in a slightly tilted slab tray so that the gravity will act on the rw's built in tube like structure and pull air down into the medium by capillary action as the nutrients are drawn downward by gravity. In a run-to-waste system rw cubes on slabe is a fantastic working combo.
But as an e&f medium the bigass six inch cubage just blows chunks imnsho.
That being said...it's not doing the plants any good sitting in those sloppy wet soggy clunkers.
So I'm wondering, whether or not the roots of these seedlings have started to grow out of the big cubes yet and if so how much ?
There are a few people who actually like big cube rw on a flood table, not many after they see how well e&f works with the right kind of medium.
RH is relative humidity. And did you soak the rock wool in wter at ph 5.5 to alleviate the superhigh out-of-the-box alkalinity of rock wool? Maybe alkalinity in the root system affecting nutrient uptake/causing deficiency?
