Brown and yellow spots on seedlings leaves please help

[novakov23]

Hi there I m running some mixed strains from seeds in soil (bioterra plus) with 6.5 ph`d water...Temperature 25 degrees and RH 55-60%..I didnt give them nutes yet since they are 15 days old...Unfortunately I noticed this yellowish spot only on two plants at first and then in two days they spread out to other 4...I read every single guide about pest and diseases but I could not find any similar issue..any idea on what would it cause this?...it seems also that they stopped growing! The 3 set leaves matured very quickly but the 5`s are taking too much time it has been 4 days now without an evident growth..any suggestion and help would be appreciated, Thanks a lot to everybody!https://www.icmag.com/ic/attachment...nt.php?attachmentid=260558&stc=1&d=1396004045

 

[jslay]

Looks like a CalMag problem.