Apologies for reviving a dead thread.
@jHands did you ever solve your problem? Running an extremely similar soil under LM301b chips, been having a time of it. Similar to you, soil outside is rocking their socks off, inside not so much. Almost presents as cal/mag issue, along with slight purple streaking on stems. Running a 3x3 with a fabric bed roughly a foot deep, under a 400 watt unit that I haven't been able to blast em with yet due to obvious issues. It seems it's a distance issue to me. . . . Moved the chips to 24" seemed to get me a deeper green (albeit not gone either). Biggest difference I see between the two systems would be temps/humidity & I dont run a blumat. FWIW, my temps stay between around 64-68 at night and get around 74-76 at lights on @ canopy (doesn't break 82° at the light level, at the dirt under a thick canopy it rides at 71-72 all day)