Can't get seeds to sprout in rockwool

Greetings! I am trying to get my first hydroponic grow started. I have been trying to sprout some seeds in rockwool and have been thoroughly unsuccessful. I have grown many crops in jiffy pellets and soil previously but cannot get a single sprout in rockwool. I soak them in water until a small taproot appears then plant them in preconditioned rockwool (previously soaked in 5.5 pHed RO water.) When I dig the seeds up, some have a brownish discoloration. Many can’t shed the seed cover and are very pale (and dead).

I’ve never used rockwool, but sounds like maybe a little too much water or light may be hitting tap root.