I agree it is some kind of defficency, with the medium you are usesing, if no dolomite lime was added before you should add some to the top of the pot now, also if your soil has dolomite in it, then mabey try some cal/mag. the soil ph and wter ph should be at about 6.0.

test your run off from the pot and also test the water ph before feeding. they should be realy close 6.0, also since your plant is already sick, some enzyms to help the roots would be a good idea, hygrozyme, and sensizyme is available localy or cannzym is available for about9 bucks at BGH. ph being off can stop the plant from taking in nutrients so look at ph first, then look at adding suppliments, or you could make things way worse. thats a very nice bush buy the way, if your a new grower your doing great