Garden Pests and Diseases: Borneo Giant doing poorly please help!, 1 by kahoona

kahoona wrote:
Hi
I am really impressed with Borneo Giants but can't seem to grow one. I planted this one around a year ago in December as a small plant ordered online. For 7 months the leaves got bigger until they hit around five feet tall. For the past six months they are getting smaller and not lasting long before they turn a patchy whitish color and then slowly wilt. Each one is smaller than the last.
I am in North Palm Beach, FL. Our soil is sand amended with County Compost (sewerage sludge and yard waste composted) and leaf litter. It is somewhat alkaline. The garden is lightly mulched.Drainage is almost too good. The plant is in light shade but does get several hours of our fierce sun each day.I used a large amount of balanced fertilizer and also regular 6-6-6 in the beginning. I also added miracle grow at low levels in the watering system. Our rainy season begins in August and I was gone during August and September so there was no fertilizer then. It can rain up to six inches in a day during those months but more normally two or three inches three times a week. The Miracle grow restarted in October and I started adding time release and 6-6-6 again in November. The Alocasia right next to it is not a Borneo Giant and is doing fairly well with no white patches. Nearby is another named "Stingray" which has the same problem.
I know that our rainy season can wash all of the nutrition from our poor dune sand and that heavy feeders like this need help but the white on the leaves is disturbing. Any Idea what it is and what to do? Here are some pictures. I really expected it to be 8 or 10 feet tall by now but it was down to 3 feet and is now up to 5.
Rob