Mold, Bacterial Bloom, or Something Else?

[CrabberWill]

I recently noticed this against the glass on the side of my crabitat. I've kept an eye on it, and it does appear to be slowly getting bigger, so I suspect that something funny is going on in there. There are other spots of the same substance around the perimeter, but the highest concentration is here. This is in front of and beneath the freshwater bowl, but the chopstick method shows no evidence of flooding.

This doesn't match any description of a bacterial bloom that I've seen here--it's not gray/green, there's no sulfur smell when I stick something down in there, etc. I'm guessing that this is mold, particularly given that it seems to be concentrated in areas of the sub that are a bit more heavily skewed toward Eco-Earth than sand. Of course, I don't know what might be going on in there where I can't just see through the glass.

Neither of my crabs are down right now, so I don't have to worry about that. I've read here that mold isn't as big of an issue as a bloom, but either way, I plan on tearing down and replacing the sub because I just don't like the idea of it being there. My question is if any of you have seen something like this before and if you can tell me exactly what it is so I know what I'm dealing with in the future.

https://imgur.com/a/KZSlAQx

[wodesorel]

I think it's mycelium - fungus. It grows like this for a while, sometimes up to a year, before putting up mushrooms. It is harmless to the crabs, but it won't stop spreading unless you add springtails or let it dry out completely.

It sets my allergies off something awful so when my tanks show signs of growth, I gut the tank, sterilize everything I can with bleach or boiling water, and set up again with fresh substrate. And it can come from anywhere, I've even had bags of pet bedding come from the store growing it.

[CrabberWill]

Aaahhh... I never thought that it might be a fungus! Thank you!

It's a relief to know that it's harmless to my critters, but I'm still going to get rid of it. I don't have the allergies to worry about, but it's the principle of the thing: I'm not having anything growing in there without my permission. I picked up a couple bags of play sand and some fresh Eco-Earth on my way home from work today; I have tomorrow off, so that'll be my project. I've been thinking about going some redecorating in the 'tat anyway, so this will give me an excuse to do that while I'm at it.

[Sunshineandcrabs]

Hi! Have something similar happening now, any word on how this turned out?