HCA: Hermit Crab Association

Hey guys. Tank has been set up for about 3 months (my girlfriends) substrate is just play sand. It's been dry so we've occasionally poured water in it and mixed it to try to moisten it. However, the sand now has large green patches in it visible on the walls of the tank, and there are some green clumps on the surface that we've always scooped out. We have never seen the green underground before. What should we do?

This is algae and it means that your substrate is getting oxygen.

If it were black/grey and smelled like rotten eggs, you would have a bacterial bloom (anaerobic bacteria that does not exist in the presence of oxygen) and that would be bad.

The algae is harmless and your crabs will probably pick at it and eat it.

If you are having issues with keeping the correct consistency, I suggest mixing some Eco Earth (coconut fiber) in with the playsand so that your substrate will keep it's sandcastle consistency without the need to constantly pour water on it, which again, can lead to flooding and the bad kind of bacteria.

If any members that use only playsand want to jump in with tips and tricks, I'm sure they'd be appreciated!

Get rid of it! You've got mold!!! Sand does not absorb water. It just sits there and molds. That's why you use eco earth to absorb the water.


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MsWorld wrote:Get rid of it! You've got mold!!! Sand does not absorb water. It just sits there and molds. That's why you use eco earth to absorb the water.


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This is not mold, it is algae, and is perfectly safe. Many members do not use Eco Earth in their tanks and they have had no issues with straight playsand. In fact, some species of crabs, like Aussies, require almost nothing but sand in their setups.

Update: the bottom of the tank is covered in black splotches. I imagine this is the bad bacteria. Doesn't stink, but I have yet to dig down that far. Will I need to replace my sand?

I would just order pre mixed sub from hermit crab patch it's an easy quick way to get perfect sub with out guessing and yes that sounds bad id change it right away though

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beastyhylian wrote:Update: the bottom of the tank is covered in black splotches. I imagine this is the bad bacteria. Doesn't stink, but I have yet to dig down that far. Will I need to replace my sand?

Can you post pics? Do you have molters down?

You can turn your substrate over so that all of it is aired out, but if you have a bacterial bloom and rotten egg smelling substrate, it will need to be changed.

50lb bags of playsand are less than $5 and a 3 pack of EE bricks less than $10. Much more cost effective than ordering substrate online.



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Well mould is normally white or a bluish-green... And off memory, mold requires O2...? If its a green-green (like moss or forest green) its probably algae, like soilentgringa said. But, if you want to play it safe... Piccies would be good.

Here are some pics (I hope):





sorry about the glare! Also yes, there's a frequent digger and a current crab that is either molting or possibly trapped because the sand is hard. I think it should be fine as there has been a different successful molt in the sand, though. should we dig him up? No clue where he is but we have new sand and EE to replace the substrate entirely

Is there EE mixed with your sub? It just looks like the substrate is settling normally. You can just turn it over with your hand and expose it to air.

That doesn't look like a bloom. I'm viewing on mobile but it just looks like regular sub with EE mixed in.

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It's just sand, no EE. It doesn't appear to have like pockets of air under it, they're flush with the bottom

Sooo.... It's okay? I'm quite nervous still as it is only sand with no ee

beastyhylian wrote:Sooo.... It's okay? I'm quite nervous still as it is only sand with no ee

Do the sniff test. If you scoop some of the black out and it smells like rotten eggs, you have a bloom.


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