My hibiscus is losing its leaves after they turn yellow. It is in partical sun and I water about once per week.
Hibiscus Losing Leaves
Certified GKH Gardening Expert
I would be willing to bet that the plant has a pest infestation. Some pests, like thrips, aphids or mites, can be difficult to see with the naked eye. I would treat the plant with neem oil. This will kill any harmful pests on the plant without being a danger to people or pets in the yard. Here is more information on neem oil: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
Just in case pests are not an issue, this article has many of the reasons a hibiscus turns yellow: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm