You say the seedling gets very hard and dry, your temps and humidity sound ok so logically i'm thinking maybe it's not able to take up the water it needs? Is there enough moisture in your rockwool? I've never used rockwool but i remember seeing something on here about a few issues with it regarding it holding too much/little moisture.

Hopefully someone more qualified to help will be along soon

In the meantime i'd double check your rockwool procedures (soaking, watering, ph etc) and see if you can spot something

Good luck!
hudson88 Reviewed by hudson88 on . confused Having issuses getting new seeds to start and cant figure out what I did wrong. the first time we tried we started 3 seeds (1 was a freebie when we bought some and 2 were just generic that we had been saving) and had 2 survive, 1 generic and 1 freebie. Those 2 have grown into a couple of monsters which have a couple more weeks left and have been trying to start more to replace them but so far have failed on every attempt. we germ the seeds in a paper towel and that works fine. I soak the Rating: 5