What Have I Caught?

[Givmeanf]

I am in the second week of a fishless start-up.
My NO2 & NO3 are still high, and the salinity needs to be brought down a little.
I have dry 'Life Rock' from CaribSea and Live Sand from CaribSea.
Store bought saltwater.
Green algae are growing directly under the light on the rocks and brown algae is growing on my nice white sand.
I've been watching this thing for 2 days.
I know nothing about what I'm doing; completely new to this hobby.
My guess is a sponge, seems like on every website a fuzzy white thing is a sponge, but I don't know.

What is it?
Is it friend or foe?
Keep it or flush it?

 

[fishyfishy]

Does it move? Hard to tell from a grainy photo unfortunately.

I’d probably flush it if you are unsure, you started with things that shouldn’t have life on them, so who knows what/where it came from… you’ll get plenty of new things that pop up to look at and scratch your head over as you start putting living things in your tank.

 

[project1004]

Probably best to keep the lights off while cycling other than to observing the tank. You will want to introduce some bacteria and phytoplankton and zooplankton to seed your tank. That's just piece of algae. Don't introduce algae into your tank. Not initially anyways. Your tank will go thru ugly stages. Go slow

 

[wantsummora acropora]

I am in the second week of a fishless start-up.
My NO2 & NO3 are still high, and the salinity needs to be brought down a little.
I have dry 'Life Rock' from CaribSea and Live Sand from CaribSea.
Store bought saltwater.
Green algae are growing directly under the light on the rocks and brown algae is growing on my nice white sand.
I've been watching this thing for 2 days.
I know nothing about what I'm doing; completely new to this hobby.
My guess is a sponge, seems like on every website a fuzzy white thing is a sponge, but I don't know.

What is it?
Is it friend or foe?
Keep it or flush it?

The first of many uninvited guests. Kill it as a message to all that follow.