Found this in my tank. Any ideas?

[Hoov]

Hi all, found this in my 3 month old IM40 AIO. Thought it was the start of GHA but the little pod thing at the bottom made me wonder if its something else.

 

[Subsea]

At 3 months mature, your substrate looks healthy with little agae. Where did substrate & rock come from.

Look at this link from live plants.

Marine Plants in the Aquarium

macroalgae, marine plants, caulerpa, refugium substrate, marine macroalgae for sale

www.marineplantbook.com

A distinctive green algae that is in the family Ulvales. It is both a temperate and tropical species, abundant in different forms worldwide. This particular algae features long, slippery tubes or fingers rising from the center of the plant attached by a single holdfast. The Latin term "Enteromorpha" literally means intestine-shaped. It grows in large clumps at the low tide zone on mangrove roots and coarse substrate. Enteromorpha tolerates a wide range of salinities from 17 ppt. to 40 ppt. and is often found at the base of rivers and brackish water estuaries. Like other species of Ulva, it prefers cooler water temperatures in the aquarium and will not do well in temps over 80 degrees. Like other varieties, its very palatable to fish.

 

[Hoov]

Thanks Subsea, I used dry Marco rock and CaribSea pink figi sand from BRS. A week ago I purchased a Green Star Polyp and an RBTA from the LFS. I dipped the GSP in a coral dip the LFS recommended, but maybe that was the source? My Nitrates have been steady at 5 ppm but my Phosphate has recently dipped from .02 to 0. I have a snail only clean up crew.