Why are my seedlings going brown?

Have just noticed that some of my seedlings that I've just pricked out are starting to go a bit brown around the edges of the leaves.

What's causing this?

 

I'm no expert, but that compost looks to me to be far too coarse for seedlings. Could they be struggling to get their roots in?

 

I think it's either sun scorch or over heating. I agree with Clueless too, I think the compost is too course for seedlings.

 

Thanks everyone.

 

Too coarse, and I think the pots are too large - so too much water for them to drink (before they find that they are rather waterlogged). I prick out into 1"-square modules, and then pot-on to 9cm when the seedlings have put on some growth.

I sieve using 1/2" riddle for 9cm pots and 3/8th riddle for 1" modules

 

What sort of compost is it?

 

Multi purpose. I assumed I could use it for potting on my seedlings once I pricked them out. To be fair most of the seedlings have taken fine.

I realised this morning that since last year a large leylandi was cut down and I do wonder now if the now direct morning sunrise is now scorching the seedlings compared to last year.

I will have to put yet more shading up now.