Chili seedling leaves with brown tips and curling up

I planted my seeds on the 1/1/16 and they are now doing well but one of my plants i have noticed the leaves on it are curling upwards and look to have brown tips, I had a look online and there was a mention of aphids, but the plant is in a propogator and my other plants seem to be doing fine. There was a mention of the foliage being scorched by a fertilizer that hadn't been mixed properly but I haven't give them a feed yet. Do these symptoms sound familiar to anyone?

 

Could it be over watering?

 

I once had that caused by the lower part of the seed compost drying from the heat of the propagator due to the seed compost being too 'sandy' leaving the seedlings unable to cope with the warmth from the grow lights above them (or might have been the effect of having hot, dry roots, or perhaps a bit ofeach?). Only realised what the problem was when they were removed for transplanting. I've stopped using John Innes type seed compost in propagators under lights.

 

The average temp is 15 degrees celsius, on a south facing window sill so they get plenty of light. In regards to watering i have been spraying them with a mist keeping the soil moist really every 2 days. I think i might have the same problem then @Scrungee