HELP !!! yellow leaves tips ONE WEEK OLD PLANT

Hi this is my first grow and after the first week and two of my plants started to turn yellow from the top of t leaves . I use Bio Bizz All-Mix soil 20% sphagnum peat moss,35% base soil,10% high quality organic worm-humus,30% perlite,5% Pre-Mix.Two T5 grolux lights ,No nuti added and watered two times whit distillated water PH 6.4 , plants are around 4 to 5 inch away from the light ,room temp is around 15C to 25C and humiduty is between 30 and 60 . PLEASE help what is the reason my plants started to turn yellow ???? thanks

30% humidity is really low for a seedling...put domes over them(cut plastic bottles in half and stick it over the top or something)...your mix doesn't seem too rich...and the seedlings should still be using their cotyledons as they are nice and green...weird...i'd get that humidity up into the 70-80% range....

Defo remedy humidity and also I would ease of on the light a little, never used T5's but have grown TD. Might be a bit to much heat off the lights at 4 inches away. I am usually very gentle with everything from seed. When she gets going, TD grows well. Make sure you cure for minimum 3-4 weeks though to get best quaity. Tastes like shite when just dried.

I got the humidity up to 78% and the temp is 25C , the leaves of two plants out of 13 are still yellow , I still cant understand whats the problem and why some of my plants have yellow leaves tips ??? please help !