I run a 4 bulb 24" ho with a fluval 2.0 2" off the water on a 20L tank we have and the zoas still stretching for light lol and that tank is 12" high I grow my zoas in my main system under "overkill" lighting 2 x AI prime 24x24x12 tank @ 10" off water then they settle in and color up . also most places keep there zoas under LED now so putting them into a t5 system I also experience the same either they shrivel and die immed or they take off and fatten up I think its more a lighting thing after seeing that pic of your setup, oh and quit dosing that junk there is the source of your trate problem your also risking "green" water then you can pack it up and start over