Hi Sisbear..I'd stop using the Stakes..they're the worse fertilizer known to man.
Stakes only fertilize the area where they're inserted..Not the entire root ball.
I'm not saying this is the reason your fruit are browning.
I used citrus stakes once, on one tree..it died..It could have been coincidence, but since then I tossed the remaining stakes in the trash.
Did you use the stakes about, oh, 7" long? Good luck, Toni
Do youself a favor and buy regular Citrus Fertilizer. Since you're in Fl, your local nursery should carry it, if not, you can find it on Ebay and other online sites. Good luck, Toni

Is the outer surface of the fruit brown, but the interior still normal? If so, you're likely seeing the result of citrus rust mite injury. They are microscopically small -- it's hard to see them even with a good hand lens; about the size of one leg segment of a spider mite. They turn fruit a rusty, reddish-brown, or in some varieties, rather silvery gray. They have no effect on internal quality.

Why does my lemon look like this? That’s exactly what mine are doing rusty brown Spotty black looking. Also the skin is so thick when you cut them open . is that because the fruit is not mature yet? This is my first time growing a lemon tree and the first year that it actually has a good Batch of fruit on it. But they are really hard. Not sure what I’m doing wrong.

I have actually had a similar issue with my Meter Lemon tree, I am very interested to see what everyone has to say.

Mine doing the same, but not all are turning brown just some. What is the answer