What does it mean when the leaves start turning yellow on a hibiscus tree or plant? Too much water?
This is one possibility. There are several reasons this can happen, normally associated with stress of some kind. This article explains many of them and will help you decide which is likely for your plant: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm