Ah so you do think it's sunburn. I did dose it with some 20/20/20 so maybe it's some sensitivity to the phosphorus?

I'm a little confused on the ants comment: what do they have to do with getting rid of aphids?

Ants are farmers of pests - they will farm aphids for hte dew they produce. Ants will carry the aphids from one plant to another to grow their farms.

as to the sunburn - the color of the leaves makes me think that the plant was in a more shady spot previously and moved into the sun - or was suddenly exposed to more sun. Anytime you fertilize a plant, they can get a burn if the dose is too high for them at that time. Most growers suggest working up to a dosage or using a slightly weaker solution than called for on the instructions.

If the unaffected leaves at the top were present when the plant got a change in sun exposure those should have burned also. So I think it is chemical injury.

20-20-20 is a very strong N-P-K. I am acquainted with people thinking they needed to use it on heavily watered hanging baskets, to make up for the constant leaching of soil-less potting media these contained. Whether this was strictly the case or not it certainly seems that under more normal circumstances such a formulation may not be necessary. And could even be undesirable, the 20% P for instance eventually producing a toxicity in the soil.

Thanks again for the input. The burn worked its way up from the base of the plant (top leaves are thankfully still OK) so it must have been chemical burn. Ugh. Other than ample water every couple of days (we've had almost summer-like weather here in Northern California this past week), let me know if there's anything else I should be doing.

Ugh, what a rookie mistake. I'm ashamed to admit I used to use Super Bloomer on my hibiscus (15-30-15) last year. Hidden Valley has a great article on how to properly fertilize:

http://www.hiddenvalleyhibiscus.com/care/feeding.htm

sounds like the plant will survive :) live and learn - I have a few times...given my plants sunburn/fertilizer burn you would think once was enough. At the moment i am evicting ants from my plant pots - erm ew....lol. there are a couple cali fb pages too if you want to join.