Their basal fronds naturally turn brown like that. Your Staghorn seems to be doing great. I've heard they love the occasional banana peel too, but since you're already fertilizing them regularly, they're not not really necessary. I don't give any of my Staghorns banana peels, and they do just fine without them.

While fertilizers are great for them, their primary source of energy is sunlight. Those fertilizers just help the plants unilize that sunlight to its fullest potential. I place mine outside, once it warms up enough. They get some direct morning sunlight up until noon, and then shaded indirect sunlight throughout the rest of the day, and they love it.

I fell in love with these plants years ago. They're just so unique and make wonderful conversion pieces. My neighbors ask me about mine all the time.