Tiny worm-like things & fluffy white stuff on rocks... (with videos)

carolioness · Jun 7, 2021

Hi reefers,

I own a 16g reef tank since last summer, been stocked for a few months now (currently with two clowns, a hermit, a mitrax crab, a hitchhiker stomatella snail and a frogspawn coral).
In the last few months I've noticed amphipods that are increasing in numbers, which is a rather good sign I think... I also noticed spirorbis snails, who also seem to do no harm.

Last week when I was cleaning my tank, however, I found other creatures of which I'm unsure what they are... They kind of look like worms (but kind of look like they have little legs) and are a yellowish colour. Tried to use google and this very forum, but I couldn't find any good answers...
It looks like they live in the sand and the shells that are in my tank for my hermit. There are quite a lot of them, although you can't properly see them if you're just observing the tank.
Today I vacuumed the sand again and I always catch the water in a filter sock. I poured what was in the filter sock in a little plastic cup I had and there's quite a lot of those odd worm-like creatures. This is a video I took of the cup full of stuff that was vacuumed from the tank:

(the critters are mainly visible at the water surface here)

Does anyone have any idea what these are and if they're harmful?

Here's another video that I took from when I took the shells of my tank out before vacuuming:
One of them is swimming around.
If I looked for a while I actually spotted quite a lot of life in there - really small creatures moving around... Maybe plankton? But not sure if these guys I'm talking about are also something like that...

Another interesting thing: there's some sort of white fluffy, hairy stuff on some of my rocks and other things that are hanging inside the tank (like the thermometer). I already showed my LFS a video of this but they couldn't quite make sense of it. They said it's probably some sort of (hair) algae and if there's no weird stuff happening inside the tank or with the perimeters it's probably okay, which is true of course... But I am still curious if someone would actually know what this might be... It could also be fungi perhaps? But in that case I'm not sure how harmless it is.
It doesn't instantly come off when I try to suck it away with a hose (like I do with removing some cyano that still happens sometimes) but I can remove it by brushing it away with a toothbrush and then sucking it out (hopefully ;-)).
Here's a video of that:

(it's a little 'longer' now at some spots btw...)

Anyone have any idea what's going on in my tank? But most importantly: is it harmful at all or can these things just happen like they are now?

Thanks in advance!

takitaj · Jun 7, 2021

Couldn't tell what the first one is, the second is hard to see but maybe just an amphipod (does it have legs?).

I've had the third one recently. Unfortunately I don't have an ID but it was that same whispy white stuff, kinda like very fine GHA but pure white, almost clear. It grew to like 2 inches long and came after fighting a short bout with Ampidinium dinos. (Vibrant & MB7 was used) It has just subsided in the last couple weeks and lasted for a couple months. Nothing ate it. I found it in the sump too.

Sorry not much help but a bump anyways.

carolioness · Jun 8, 2021

takitaj said:
Couldn't tell what the first one is, the second is hard to see but maybe just an amphipod (does it have legs?).

In both videos it does show the same critters, but I doubt it's amphipods. Unless it's a completely different type than the ones I already find in my tank: they have much more visible legs and feelers and are kind of curled. These unknown guys seem to keep a worm-like shape (but do seem to have tiny, short legs.) They're very small so it's hard to tell (and my eyes are actually pretty good for up close, haha). They're also kind of yellowish, whereas the pods I am already used to are more of a grey / brownish colour.

takitaj said:
I've had the third one recently. Unfortunately I don't have an ID but it was that same whispy white stuff, kinda like very fine GHA but pure white, almost clear. It grew to like 2 inches long and came after fighting a short bout with Ampidinium dinos. (Vibrant & MB7 was used) It has just subsided in the last couple weeks and lasted for a couple months. Nothing ate it. I found it in the sump too.

Hmm! I didn't fight any dinos or add anything like that, but the white, almost clear stuff does sound familiar. Could definitely be the same stuff. Glad it's going away in your tank though! That's kind of hopeful.

And no worries about not knowing exactly what it is. Any answer is nice/helpful!

Ben Pedersen · Jun 8, 2021

carolioness said:
Hi reefers,

I own a 16g reef tank since last summer, been stocked for a few months now (currently with two clowns, a hermit, a mitrax crab, a hitchhiker stomatella snail and a frogspawn coral).
In the last few months I've noticed amphipods that are increasing in numbers, which is a rather good sign I think... I also noticed spirorbis snails, who also seem to do no harm.

Last week when I was cleaning my tank, however, I found other creatures of which I'm unsure what they are... They kind of look like worms (but kind of look like they have little legs) and are a yellowish colour. Tried to use google and this very forum, but I couldn't find any good answers...
It looks like they live in the sand and the shells that are in my tank for my hermit. There are quite a lot of them, although you can't properly see them if you're just observing the tank.
Today I vacuumed the sand again and I always catch the water in a filter sock. I poured what was in the filter sock in a little plastic cup I had and there's quite a lot of those odd worm-like creatures. This is a video I took of the cup full of stuff that was vacuumed from the tank:

(the critters are mainly visible at the water surface here)

Does anyone have any idea what these are and if they're harmful?

Here's another video that I took from when I took the shells of my tank out before vacuuming:
One of them is swimming around.
If I looked for a while I actually spotted quite a lot of life in there - really small creatures moving around... Maybe plankton? But not sure if these guys I'm talking about are also something like that...

Another interesting thing: there's some sort of white fluffy, hairy stuff on some of my rocks and other things that are hanging inside the tank (like the thermometer). I already showed my LFS a video of this but they couldn't quite make sense of it. They said it's probably some sort of (hair) algae and if there's no weird stuff happening inside the tank or with the perimeters it's probably okay, which is true of course... But I am still curious if someone would actually know what this might be... It could also be fungi perhaps? But in that case I'm not sure how harmless it is.
It doesn't instantly come off when I try to suck it away with a hose (like I do with removing some cyano that still happens sometimes) but I can remove it by brushing it away with a toothbrush and then sucking it out (hopefully ;-)).
Here's a video of that:

(it's a little 'longer' now at some spots btw...)

Anyone have any idea what's going on in my tank? But most importantly: is it harmful at all or can these things just happen like they are now?

Thanks in advance!