I have some ixoras that are struggling right now and have been for several months. I originally planted them about 3 years ago and they did great until Feb of this year. I have noticed heavy yellowing of leaves, sometimes turning almost white. Previous to this, many of them had a black mold, which I was told was result of an aphid infestation. I have treated these with fertilizer, fertilizer for acid lovers, compost, chelated iron, big/mite control and extra water on occasion. Is there anything else I can do?

Yikes, you have really worked hard to keep them going. My only suggestion would be to take a soil sample to your local extension office and have them test it. I would also take a branch, sealed in a zip loc bag to have them look at it so they cold make suggestions.
https://sfyl.ifas.ufl.edu/agri...