molding

I recently took a fairly large piece of driftwood out of my tank and I just set it in a large container, well a about a month later I go to look at it so I can cut it up and use it in other tanks and I notice green on it, it's kinda light not really dark. Driftwood is completly dry.is this mold...

So I've been searching for a product that is aquarium safe and would allow me to make my own aquarium decor and backgrounds. I came across this product though a bit pricey I think this is great especially if you want to design your own paludarium or background...