Bottom leaves turnin yellow, rusty and spotty

hey all in week 5 from seed and bottom leaves starting to either get rusty spots turn yellow and then die. not sure what is the cause heres sum pics of what they look liek.
if anyone could guide me to what causes this would be great.
im using house and garden coco a and b nutes. in coco mixd with perlite. round 5-6 ph nutes at 1.4ec.
cheers

heres a general idea of what they look liek

im not sure how often to feed eeither and how much to giv them each watering for example how many litres of nutes. ive been giving bout 2 litres once a day.

Looks like mag deficency or mag locked out from ph. im no expert..and no idea whats in your nutes or soil.. just what it looks like to me.