I have a large and small hibiscus. I love them but they seem very hard to keep happy. The leaves turn yellow, but they still bloom. It seems like if I water but the leaves turn yellow. If I don't water, the leaves are droopy. I guess I can't find that happy medium. The large one does not have a lot of leaves left, although there are some small new leaves coming on. It has been in the 90's and 100's here for the last couple of weeks but I have had trouble since purchasing about a month ago.
The following article should be of some help to you: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm