pieris japonica mountain fire

Bought pieris japonica mountain fire, planted in ericaceous compost in a container, plant was doing well

Was feeding other plants with tomato food and applied some to Pieries. Now Pieries leaves have gone from red/copper to green. Leaves look healthy and glossy but unfortunately have lost their true colour. I think the plant food may have changed the container's acidity to alkaline or neutral. Should I do nothing and wait for improvement (waited two weeks at this stage and no change to original colour) or should I try and restore acidity to container. I could be wrong, but was cold tea used years ago for changing to an acid soil


Thanks