Ceratopteris thalictroides

I have a question about my Ceratopteris thalictroides (hereafter "CT")
plant. I started with one CT potted plant and now have 3 -- two medium
sized and one very large. The large one, the original, has become a
wonderful "stag-horn" type plant -- large, thick stems with a lovely
branching structure with points, nothing that looks like a leaf. One of the
smaller ones has wide leaves and the other has the fine leaves, as the
original plant used to have.

What's going on here? Is the "stag-horn" look the way CT develops as it
ages? Does it have something to do with light, or iron? Another thing --
when I had less iron in the water the stems would seem to rot -- they
turned black and disentegrated -- but they would hang on by a thread and
the leaves would not be affected. When I added more iron this happened to a
much lesser degree. Is this normal for CT?

Thanks for any info.
still in sunny and cool Vancouver