Help identifying algae please

[K626]

I've searched and can't find a definitive answer on this. This algae popped up on two of my frag plugs. It's a bit tough, and my emerald can doesn't seem to touch it, nor the hermits, snails, or tail spot goby. What the heck is it?

 

[brmreefer]

Ulva Lactuca (aka Sea Lettuce).

 

[K626]

Ulva Lactuca (aka Sea Lettuce).

Ok, harmful or no? I've never had that just show up in my tanks before.

 

[brmreefer]

Not harmful. Some folks pay to get some. However, I would remove it from that frag before it shades it out.