I would suggest starting with a complete plant food in a soluble form such as Miracle Gro. The label has application instructions and rates. Slow release products such as Osmocote are also good and would feed the plant for several months. Another option is to use a turf fertilizer with a 3-1-2 ratio of nutrients such as 15-5-10. Apply it in small doses over the course of the growing season and water it in well.
The following web site offers much more info on growing hibiscus in Florida.
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