NEED HELP ASAP.... lack of iron or nitrogen or???

[PissyFingers]

Hi all, i need some advice on these hops! A lot of the leaves are turning light yellow (pic 1) and the growth has slowed down, some of the leaves have brown edges as well. They are all in slow release fert potting mix and get watered every few days, the soil is very well draining. They have had some NPK liquid fert, when they started to go yellow i gave them some Iron chelate but a week ago and nothing has changed. They are a lot of hop flowers on them, some have what looks to be brown shading on them but on closer inspection it looks more of a reddish tinge not so much brown (the 2 pic) but then theres definitely dark browning on some tips as in pic 3... thoughts anyone?

cheers

Harley