forest flame the leaves are going yellow

Have they been in the containers for long? One other question, is it the young leaves after their red phase that are going yellow, or is it older mature leaves? They may need feeding with a sequestered iron solution or even a propitiatory ericaceous feed.

And to add to the above from Fractal, are you watering thoroughly and often enough? If they have been in containers for a long time, and the containers aren't that big, the roots may be taking up most of the room, which means there's not enough soil to hold water. If they've been in pots for a while, turn them out and check whether they're potbound, repot into larger pots if they are, with ericaceous compost.