It's fairly common Andy when the fertilizer concentration is too high. Some species like aeranthos, bergeri, and especially shiedeana really take exception. They seem to be vulnerable to green-banding even if the dilution is a teaspoon over the normal rate. Happens to me fairly often and is nothing to worry about. I just starve those species mentioned above = problem solved!

Thanks Gonzer. Settles my curiosity. Although it is kind of a cool look...

Andy, I forgot to mention that the bands are also caused by fert solution sitting in the center of the plant, not drying out completely. Always feed early in the day.