SICK SEEDLINGS?? 3rd go

Hey can anyone give me some ?

third grow ever. first 2 successful enough. pc case 50w 6400k cfl to start, 18/6 running at night. soil straight potting mix, no slow release ferts. bagseed.

this time seedlings seem to be going slower than other times. 2 weeks since pushing through soil. growing slow, one is curling leaves under, with slight brown tips on leaves (my camera is shit and couldnt capture it so no photo of this one) and slightly yellowing from outside in. the other seedling has almost white outer edges of two new leaves. both seedlings have yellowing streaks on the first two rounded leaves.

only differences i can see between first two attempts and this one;
1/diff soils. originally used my own mix of old garden soil, peat, perlite, and parents compost. this time just straight potting mix from shops (no added ferts type)
2/ different season. its winter now. current temps around 16 to 18 degreeC at night. 20 to 25degC in day.

im not too bothered, also know theres a chance i might be trippin but its doing my head in, and just curious to know lol

anyone have any ideas. cheeers!!

your soil has too much nutrients, the white salt build up on the top is a give away

Buy a soiless medium... its nute burn

Rockwool

coco coir

PC grows are awesome, but I think the white on soil is mycorizi or some kind of benificial bacteria, I get that on stuff I buy from lowes..but how often do you water?

Soil is too hot. There's no way a seedling that size would get N deficiency so the yellowing/curling is from burn