Needs repotting - that pot looks relatively shallow, so give it something a fair bit deeper and wider. Its not ideal to repot when flowers are forming, but if you're careful with the roots, it should be fine. Turn it out of its pot, carefully,and check whether its rootbound.

Multi purpose compost will do, but John Innes No 3 would be better - or a mix of the two.

And don't feed with Sequestrene... personal I wouldn't use Tomorite either on a shrub.

I agree with what Moongrower said - sequestrene is unnecessary, and tomato food is not an all round fertilizer suitable for shrubby plants like yours.

Thank you both. Have been told in the past they can cure micronutrient issues. Hmm. Do feed it as well. Will try and repot. Wish me luck!

You have to remember that the topgrowth of a plant is only ever as good as its roots will allow - if the roots are constricted, then the topgrowth starts to suffer, and the plant is more likely to suffer diseases.Repot and see how it does.

I have repotted as you advised. Flower heads are developing as usual/normal so hopefully it is and will be ok. The flower heads are definitely not as floppy either. Couldn't believe how dry it was when I repotted it either. You think you are dosing them with water and that was definitely a lesson learned. Thanks so much everyone.