Of course it's difficult to tell what's wrong w/o seeing it, but it could actually have gotten scalded from the sun. Also, hibiscus don't like to be moved, even if it's to a better location.

Mine did that too. Especially after I bought it at lowes and transplanted it. It also did that if I didn't water it everyday.
But i hade heard that too much phosphorous (like in bloom booster) can over time, build up in the soil and poison the plant. i use MG Bloom Booster myself, but not too often.

I would highly recommend not using any bloom booster product, as they typically use high amounts of phosporous, which Hibiscus do not like at all. It could in fact be the reason that your hibiscus has yellowing leaves. I think it's probably the combined stressed of being moved to a new location and having to adjust, in addition to the phosphorous, which is causing the yellow leaves.

Every time I bring home a new hibiscus, they go through a period of yellowing and leaf dropping, until they adjust and fill out again. I've also noticed that the rarer cultivars bought from nurseries have a tougher time acclimating than the kind you find at home depot or lowes. I suspect that it's probably because they spend more time in a green house, under near perfect conditions and are subject to less stress.

Thank you all for the excellent diagnosis. I've stopped with the Bloom Booster...and yes, the yellowing has stopped!
This plant did come from a nursery...can't find the tag at the moment but it is some fancy variety.
Which fertilizer would you recommend for hisbiscus???

www.yardgeek.com has a great hibiscus fertilizer. So does hiddenvalleyhibiscus.com