White moldy stuff on sand bed

[Teen reefer]

Hello, I was looking at my tank this morning and I see some kinda moldy white stuff growing on the sand bed and I wanted to know should I remove it and is it bad?

 

[DDenny]

When in doubt take it out. But I have no idea will leave that other.

 

[Teen reefer]

Well I will do a water change tomorrow and see if it will comes back.