You have to decide whether the little black specks are actually black spot or not - if they are, you need to treat with a fungicide. Try Roseclear 3, mixed up in a sprayer according to the instructions on the box.

Hi Bamboo - could this be black spot and over watering?

I'd have thought overwatering very unlikely, unless its growing in a tub without drainage. We also don't know what Guest sprayed with in the first place, nor do we know whether the spraying was carried out in bright sunlight, which would cause these problems, or certainly contribute to them. The little black specks could also be anything from mud splash to blackfly to leaf spot to black spot, or a result of growing in the wrong place, so hard to say any more really.

Thanks Bamboo