Posted: 10/04/2016 at 10:05
I think it's as Fairy described, too warm and wet. I've just moved my only indoor tray outside as I was having trouble with this too. I've taken the lid off as well to get some more air in. Mould on compost is not good news for any emerging seedlings. What are you growing? Might be worth starting again and trying to keep the compost drier.
I get my seed tray, water from the bottom, so the compost is just turning darker. I then sow my seeds, and cover with dry compost.The wetness should seap up so no need for further watering.
If I think the soil is drying out a bit before the seeds are up. I spray the surface rather than use the water can. Most of the time this works well for me