What is it and why is it there?

[Kmsutows]

Welp my alk was low and I have been slowly raising it... during this time I've noticed this green algae covering my rock and some sand. Any insight? My nitrates were undetectable by the way... first time I've used the test so maybe I did it wrong?

 

[Shaddow_wolf169]

Looks like moss I would be worried about the mushroom so close to the zoas it will sting and kill them. Nitrates ad phosphate could be present but the algae is sucking it up to quick to test right.