I have come to the conclusion that it is not a simple problem caused by one thing. Keep in mind this is new sod put in at the last of July. No herbicide was put down prior to the installation. Shortly after the installation there was a mole cricket and chinch bug infestation. They loved the new sod and moist conditions but were quickly controlled. There was also a I think a toxic drip coming from the palms near the pool also which weakened the sod, probably wouldn't have been a problem on established grass. Weak sod and the moisture from August-Sept S. Florida tropical rain makes conditions ripe for fungus infestation. Unfortunately the rain also washes away fungicides in this sandy soil. It was treated with a granular fungicide 4 weeks ago and we'll treat again this week and see what happens.
If I had to do it over again I'd establish new sod in the spring in S. Florida when you can control the conditions a little better as far as water is concerned.