I added couple of rocks and I noticed some white soft stuff growing on my rock

[Yadhu]

I just started up an old 10 gallon tank because my Molly is prego and I wanted to keep a nursery tank ready once the fry drops... I added older plants and decorations from my current tank to get the tank cycled faster. However I added couple of rocks and I noticed some white soft stuff growing on my rock... I'm wondering of this is some kind of a sponge...? I need some help confirming this and if not is it harmful? Thanks guys!

 

[librarygirl]

Hm, I have no idea. So there's nothing live in the tank (fish or snails, etc)? Did you add the rock from outside or from another tank?

 

[Yadhu]

I have one ghost shrimp in the tank. I also added a few hornworts (spelling) from my older tank. The rocks were given to me along with the tank from my friend.. havent asked him if he used it before or just found em outside.. although, the white stuff is turning reddish... is it red algae? some amount of sunlight does hit the tank around 1-2 PM