Is this a boron deficiency?

[FLlover123]

I have 4 large Sylvester palms. 2 are in front and 2 in back. My 2 front ones started shedding leaves and on 1 of them, the center growth looked stunted making the palm saucer shaped. We thought it was squirrels and attached a piece of metal around the tree to try to keep squirrels from climbing it. A landscaper who happened to be riding by stopped me and said he thought it was a boron deficiency. I keep all of my palms fertilized on schedule with Lesco 8-2-12 palm fertilizer that contains 0.15% water soluble Boron.  After treating the 2 in the front with Boron this past May,  they appear to be recovering nicely.  Fast forward a few months and now the 2 in our back yard have leaves on older fronds not looking good.  One of them is dropping leaves just like the front one did. 

We have an irrigation system that filters out iron with a chlorine injector (due to iron bacteria stopping up sprinkler heads).  We are wondering if this is affecting our Sylvester palms. Does anyone have any ideas?