yellow leaves in fifth week from seeds

HELLO

I might need some edvise I' d say. My plants starts turning yellow and purple . I have prepered everything correctly:
-soillex mix 33% peat moss, 33% vermiculate, 33% perlite
-temperature at first was a little bit low 15 celcius (some curled leaves)-so i havent prepered everything ok :( but in fourth week goes to 23 celcius and stays.
-humidity 65%
-envirolite 6400k ,3500 lumens per plant
-after 3 weeks transplant them to 3 galon pots- less stress in the future- and use dilute fert 1/3 ( I use tree fern feed 26:6:11 with magnesium oxide soluble in water 1.6%,mg=1%.
-medium keeps water well, second watering after 8 days,used dilute fert 1/2 and stil no help
-water I use is soft tap water
The only thing I am concern about is the hydrated lime in my mix I made myself (Jorge Cervantes' tip in Bible) I couldnt have got a dolomite one at all. I put about 1/3 cup in 1 cub foot.
Ph of the medium is perfect 6.7.
Help me please.

Some pics would be helpful. If you can't post pics could you describe in a little more detail the symtoms your plant has. Where is the yellowing? Is it the bottom leaves or leaves all over the plant? The purpling, is that the stems or the leaves?

If it's yellowing bottom leaves and purple stems then the plants aren't getting enough N, now that could be that there is a nute lockout, flush with plenty of water and feed with 1/4 strength nutes.

Good luck!