Please ID this "Fern"...

[netspace]

I have 14 G nano cube and for some time I noticed a small one inch green fern growing at the top of my tank - could you tell me what is it?
...a few months before that, I noticed a green grass that now is somewhat controlled by an emerald crab...have happy holidays...kris

 

[StephLionfish]

The 'fern' is Caulerpa mexicana. Not very hard to control, but will go sexual easily. If you like it, keep it trimmed, and don't have one long strand. Have several, so that when it does go sexual you don't have to pull out as much. I have a tank full of it, and some went sexual the other day, and I just pulled it out and tossed it... The growth rate isn't too bad. The mexicana can get leaves/blades as long as a foot.

The 'grass' looks like some sort of Cladophora.

 

[netspace]

thank you for your help...

 

[cubsFAN]

I think it looks nice, but it can spread quickly. I used to have a tank full of that and mushrooms. It looked great, but it's not what I was going for. It took a long time to get rid of it. I've still got some of the shrooms.

 

[StephLionfish]

Is one of those stars a sandsifter? I hate to say it, but those don't survive long. There's simply not enough food in our sand beds to feed them. They eat all the good animals out of the sand bed, then starve..