Is this a type of algae???

[Rocky998]

I didn't say there was...my point was that the type of mold that can grow in damp places behind the walls of a bathroom that has a leak from the shower or tub (as an example) once discovered can cause very serious sickness to people. Obviously this mold is not "safe." That doesn't mean the mold (if it is mold) on the wood in your tank is toxic, or safe, whichever. You have to realize the possibility and be aware of it.

The toxic fungus that can appear on some types of wood is deadly. That is fact. So be cognizant of it, and don't shrug it off. You don't know, and nor do I.

I will be cleaning it off during the large water change I do near the end of the cycle...