Lower or upper leaves? What kind of mix did you pot into? What is the sun situation and watering situation? How are you providing nutrients? Lets start with these and see if we come up with some possible ideas as to what is going on.
Happy Growing David

It is primarily on the lower leaves. I used miracle grow potting soil, and no fertilizer as of yet since the soil already had some in it. It is in full sun. Maybe that is my problem since the sun is so brutal here in FL. I have moved it into a sunnier area since potting up. The soil has stayed pretty wet lately because of heavy rains. It just can't seem to dry out. I also started noticing what I think are spider mites today. There are tiny insects with thin webs on the backs of the leaves.

Probably too wet is the most likely culprit for the yellowing leaves, but the fert in miracle gro is not anything to count as fertilizing for a heavy feeder like hibiscus. Many a hibiscus grows in full sun so I doubt that is a direct problem . The mites will need to be dealt with before they get any worse. They usually show up here in Texas as it drys out in the summer. Haven't seen any this year with all the record rainfall we have had this summer. Get the hibiscus under cover if too much rainfall won't allow the hib to dry. I can't say I go much for miracle gro potting medias myself I usually make my own mixes fro m scratch or modify any potting mixes to give them better areation. I have work with most of the potting mixes out there at one time or another and still feel that I have to amend it to my purpose to get a better result than the straight stuff. Poke some holes in the soil if need be to get some air to the root system and look at a regular feeding regime would be my starting advise and then if you can't control the rainfall issue and can't get the soil to dry adequatly them consider repotting into a fluffier mix with more perlite if nothing else that will insure better drainage and better air for the roots. You may have to water more when it is hot and dry but that is better than having roots rot because they are to wet. That is my opinion and many on the container forum would vouch for that same thing. If you are interested then check out the container forum a great resource for any hibscus grower that uses potting for their babies.
Good Luck and let me know if I can help in any way.
Happy Growing David

Unless your soil is waterlogged, I am thinking it may be the mites. My potted hibiscus are incredibly thirsty plants here in New Jersey. I have a number of varieties, including a double mutabilis from Samoa that got about ten feet tall and eight feet wide in my garden. Mutabilis plants do better in the ground since they need quite a bit of water which is easier for them to find when their roots are free to roam! My mutabilis 'Rubrus' plants also get about ten feet high here in southern New Jersey. I am even trying a Cuban Hibiscus. It is as spiny as a rose!

Thanks for the advice. I'm going to start treating the spider mites and then go from there with the rest of the suggestions. Thanks again!

I bought 3 Hibiscus that were in beautiful leaf and flower. I transplanted them in an indoor solarium with 4 skylights.
They were doing great for the first few weeks and now the leaves are turning yellow and falling off.In fact one of them has no leaves left on it at all.If anyone could offer any help as to what is causing this ,it would be most appreciated.

John