How do i fix a Zinc Deficiencie??????????

[orlcorekid]

Three of my plants seem to have a zinc Deficiencie. Can some explain to me how to fix this problem and why it occurs? Thanks

 

[orlcorekid]

Hydro=Ebb and flood
400 watt super hps (hortilux) 3' away 24/7
1/4 (botanicare plant engery products) pro grow 3-1.5-4
1/4 (botanicare plant engery products) sweet 0-0-0
75* night-85* day
40-50% humidity
30min on /3 hours off
ph 5.5-6.0