Phosphorus deficiency???

On my first grow and need a little help...

Can't figure it out, I'm using 19N 6P 12K Osmocote Smart-Release plant food and watering with diluted 2-3-1 seaweed & fish fetilizer. My fan leaves have purple veins and are a little blue-green, my stems seem to be getting a little flimsy - though it may just be my imagination. Should I be looking for another mix to feed my babies? I'm a little concerned about the "smart-release" and the possible effects on PH and the risk of over-fertilizing. I heard some strains are naturally purplish but I think it's too great a coincidence to have all 6 from bagseed being this way.
Oh and I got Aphids annoying me, anyone know a good way to get rid of em?

personally i dont see much of problem but one on left of pic... a lil curled and i might see a tip burnt.. other than that theyre nice... an alright ration on nutrient which youre feeding.. but i dont see phospohrous being your problem.. if this is a pic of their morning light id say you could see improvement throughout mid time of light but you could wait and see what others say...