leaves turning mottled gold!!! HELP!!!

hi, im having a problem with my 4 very young seedlings, basically quite a few leaves have started to develop a gold/dirty brown mottled effect? not just at the tips, it seems to be on the bigger leaves, its almost like some one has sprayed gold paint on to make them look old!!
ive just gone to water them and under the light you cant really notice, but once in normal light its very obvious,
they are 4 weeks from germination, in their second pots which i transplanted about 10 days ago, (6" squares) they are in biobizz light mix, growth has been great up till now, nice colour etc ive 4 under a 250 cfl, and was looking at putting under my 400 hps soon as i want theese as mothers (hopefully) to cut for a planned sea of green, last watered 2 days ago and that was the first time i fed them just 1ml bio grow and 4ml rhizotonic
they are blue mistic from royal queen and ive had success with them before and never had defs or burn,
ive tried to take pics but its very hard but will take in daylight tomorrow, believe it or not camara on phone has done better then my digi, so will post theese for now but they are not great sorry!! ive scanned for mites but no signs of anything like that, am wondering if i fed to early, or if they need more??? temps are good have a small fan on them but not a tornado!!! any advice would be great,
cheers
cozz

sorry heres some bad pics, also ph is good, using fridge filtered water(cocanut husk)
thanks

Get some Cal Mag. Looks like a deficiency of some sort.

cheers for the input, without sounding stupid would using cal-mag do anything bad? ive never used it thats why i ask, or is it a case of trying things and flushing if it gets worse?, i was under the impresion that bio light mix whilst not a hot soil should have enough for a couple of weeks, obviously somethings not right though, just never used cal mag,