[drythropple]

What is making my compost go green? Am I doing something wrong, the compost in my seed trays has gone green on the top, I dont think I have over watered

[paintedlady]

it sounds like algae - a combination of warmth, moist surface & sunlight.  That often happens to me when I've got stuff in the greenhouse 

[blackbob]

What is making my compost go green? Am I doing something wrong, the compost in my seed trays has gone green on the top, I dont think I have over watered

spray the seedlings with cheshunt compound and use vermiculite to cover them over.
i bet you used water out of a rain butt.

[Kristen]

I cover my seedlings with a thin layer of vermiculite (rather than nothing / seed compost) and I only water with tap water (cleaner than rain water, as blackbob says - once they get bigger I give them rainwater). I soak the seed trays in a Cheshunt Compound solution before sowing, and then cover with a transparent cover (or put a pot in a closed clear plastic bag), and generally I don't have to water them again until they have germinated (at which point open the bag / clear cover for a day or so and then remove it).

[pink aubergine]

I think it may be lack of circulating air. You dont say where your seeds are- on a windowsill, in a greenhouse etc, but I would have thought that if you open them during the day on warm days, or put on a cover with vents that open in the day, or put a plastic bag over the top but dont seal it, you will have less problems.

In the end its down to the compost. I'm using Levingtons multipurpose with has added John Innes, and I've had no prob with algae. However some of the specailist seed composts have developed this green on top. Its all a juggle between not drying out too quickly and holding onto the water for too long - but thats what your problem is.
I would recommend opening up the pots and watering with fine rose only when necessary. Should be easier ast this time of year as everything romping away!!