Two containers have algae in them. Now it is the lithops which I am pretty sure are never going to germinate but I don't know why it has popped up, I used a anti-rot spray on the soil before I started. Any tips?

The green growth you speak of is common and not a problem for your seedlings provided it is kept under control. Many seed trays will develop it, not just on top but throughout the soil. Give the soil a drench with a fungicide if your worried about it or if it starts to grow faster than your seedlings, you don't want any competition.

OK I will leave for it for a while, thanks for the tip!