one is quite bad, one is slightly affected and then the last one is doing great, wish I had caught this earlier fingers crossed it won't affect the bud. Check out my pics on my journal if you want, I'm pretty chuffed with them all to be fair 
thought mag problems were only in coco mainly, i use coco with hesi coco feed and have lovely green plants but know some prople using canna get same problem......I'm in perlite, around the 10l bucket size. I went to my local hydro store and he didn't have any, he told me to get some epsom salts. It's a bit annoying, out of the 3 in flower only 1 doesn't have this yellowing