do my Dark devils need more food?

[Muddy]

Muddy its runs warm inside the average is 27 30 cel with lamps on and 25 to 19 cel with lamps off. I feel like your on target with iron issue. i have other Dark devils total of 4, but only the two purple phenos have this issue. the other dark devils are very very green along with
the delicious cheese candy and the Buddhas are all fine and live in the same soil and get the same nutes...

Temps are good. I can see the red stems and red on the new growth and wasn't sure if it was temp related. Sometimes red stems can indicate a lack of P from lockout or low temps, but in your case, it appears to be genetic, related to the purple pheno. Just wanted to make sure.