Gray Mold IN Rockwool??

I placed 4 seedlings in rockwool in my DWC a few days ago... I just decided to replace one with another seedling that seems to be doing much better... When I took the plant out, there is this gray mushy mold all over the bottom of the rockwool?? IS this mold, mildew? I know it's not algae...and it's definitely gray.....Does anyone else have this problem? how can I fix it? are they getting too much water from the drippers? should drippers be on 24 hours a day..that's what I did for my first grow but now I'm not so sure maybe I should have the pump on a timer so drippers aren't going all the time?

Sounds like mold to me. I hate rockwool.

I would put them on a timer. I run a Aero flo ripoff home built. I run my pump 30 min on 1`/2 hrs off. Works for me. gives things a chance to dry out and get some air. I don't know just what i do. I know rockwool holds a lot of water for a longer time than you would think.