rockwool blocks gone slimey

hi, i have got a problem with my seedlings, there in 3inch rockwool cubes in a tray under flouescent lights.
ive just bin feding them ph'd water with a small amount of liquid oxygen with i always do but ths time something strange is happening.
when i pick the cubes up they have a slimey feel to them and there dosnt seem to be any roots appearng either?

if anyone knows wot is causing this could you please help as its really doing my head in now lol

thanks
ishy