What is this?

[TeeJay]

I'm guessing it's black hair or beard alge. What's the best way to get rid of it.

[lefty o]

if you are talking about the fuzzy stuff hanging off the leaves, thats the roots to the baby plants that are growing. i see nothing wrong in that picture.

[Plant-master]

Yeah those are new plants developing. Since the Java fern is a rhizome plant it sends off runners. Eventually when they get bigger they will come off and you can attach them to hard scape. 

[Minanora]

Baby plants! Those are roots from babies! Huzzah! Your easy planter could not contain the life! 🙂 You can attach them to plant weights, rocks, wood, whatever! ❤️

[Apulo]

I'm so glad I saw this, I have the same going on in my tank and I was about to do a hydrogen peroxide dip lol

[Odd Duck]

Yep, baby plants!  Remember that Java ferns are, well, ferns.  They develop spores like terrestrial ferns but they can’t scatter them as well as terrestrials.  So they often sprout while still attached to the leaf and you get this, where a baby plant develops right on the leaf.  Once the roots are about an inch long, you can usually gently pluck the baby plant off the leaf and attach it elsewhere.  Java ferns can and will scatter spores within the aquarium, too, and if they manage to lodge someplace, they can sprout and baby plants will randomly appear.  It can be hard to tell when this happens if it was a sprouted spore or a tiny baby plant broke off and drifted.

Don’t be surprised if the big leaf goes bad.  Sometimes when the spores start to sprout and make baby plants it’s triggered by the big leaf starting to go bad.  I’ve been known to keep those dying leaves floating around so they produce more babies.  But I have plant holding tanks that don’t have to look pretty that I use for that.