Are My Seedlings Doin' Alright?

hi guys ,
this is my first grow,ive got a nice setup in my attick ,its got a 400watt hps son t lamp a fan and a hydro/temp meter,,oh ye and dont forget the 4 snow white feminized babies 12 days into there grow!they are about 4 inches high and are only starting to get their second set of leaves now!are they growing too slow??the tempatures are highs of 22 degrees (celcius) and lows of 7.5!is this too low??they look healthy only they have leaves that are not too dark green they are light green that ok??any comments wouyld be greatly appreciated!!tanx
 
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