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I apologise if this isn't the correct place to post this.

I have a well established 5' x 2' x 2' tank with a large elderly Gibb, an Agamyxis and a couple of dozen mixed Corys.

I recently noticed very small flies buzzing around the tank, which I identified as fungus gnats. I strung fly paper at various points over the tank which successfully caught loads of the little shits, but then I realised they are actually laying eggs in the water (even though I had a tank lid on), which are turning into wormy larvae which live in the gravel. I have been hoovering out a couple of buckets every couple of days and wiping all the cover glasses and tank edges, and the Corys are doing their best, but it is a war of attrition at best. Has anyone else ever had this problem? The tank has been set up for 15-20 years and I've never had a problem like this before. Because of the size of the Gibb, running a quarantine tank hasn't been possible so I can't move the fish elsewhere.

Hi Alison M,

I've found moth flies in my tanks. Same type of problem. It's really a nuisance issue and as far as I know poses no harm to the fish. I've only beaten them back with more diligence on water changes.

How coarse is your gravel? Are the corys able to dig in it for the larvae without you needing to collect them?

Good luck, Eric

Duplicate post

Hi Eric, thanks for your reply.

The gravel is largish (not quite pea size) but smooth - the corys can dig but it's probably about 5cm deep at least, so they can't get to the bottom. I did think about reducing the amount of it, but that'd be a big task.

Did your moth flies eventually go away, or did you have to live with them?

Hi all,

Alison M wrote: ↑17 Dec 2020, 14:56I recently noticed very small flies buzzing around the tank, which I identified as fungus gnats. .........realised they are actually laying eggs in the water (even though I had a tank lid on), which are turning into wormy larvae which live in the gravel. ......

They are entirely harmless to your fish, in fact they are a preferred food item for small tetras etc. I feed my small surface living fish with the, very similar, <"Sciarid Fly"> adults.

They aren't Fungus Gnats (all gnats look the same), they are one of the Aquatic midges, you have a wide choice of <"biting"> and <" non-biting ones">.

I'm going to assume they are non-biting (if they were "Scottish biting midge"(Culicoides impunctatus), I think you would know straight away).

bekateen wrote: ↑17 Dec 2020, 15:56 ....... I've found moth flies in my tanks.

You can definitely reduce these by increased tank maintenance, they are very much associated with <"organic biofilms in damp situations">

cheers Darrel

Hi Darrel, I will look up look up the various midge types - they definitely don't bite, being thankful for small mercies!

I don't have any tetra type fish (accidental incorrect overly aggressive cichlid purchase), but there are loads of the damned things in the gravel, and flying in my sitting room. Even if the corys are happy to eat them, having them fly up my nose every time I go near the tank is really annoying.

Pity I can't package them up and send you them

Hi all,

Alison M wrote: ↑17 Dec 2020, 16:22Hi Darrel, I will look up look up the various midge types...... Pity I can't package them up and send you them

They all look the same, unless you have a dead one, a taxonomic key and a dissecting microscope.

I'm actually better with IDing swimming larvae, but then only to family. "Biting Midge" larvae (Ceratopogonidae) are tiny, but really long and thin (like a Tubifex worm) and swim with a snake like motion.

I might try a bit of gravel vacuuming? I'm not a user of gravel (only sand), and I only have planted tanks, so I don't have any practical experience of removing them.

Alison M wrote: ↑17 Dec 2020, 16:22...... Pity I can't package them up and send you them

I get a few out <"the buckets that I use to culture"> Blackworms and Asellus. When I had more fish I used to make more of an effort to <"ranch" Bloodworms"> and those buckets would produce a lot more midge larvae.

cheers Darrel

Alison M wrote: ↑17 Dec 2020, 16:15 The gravel is largish (not quite pea size) but smooth - the corys can dig but it's probably about 5cm deep at least, so they can't get to the bottom. I did think about reducing the amount of it, but that'd be a big task.

Did your moth flies eventually go away, or did you have to live with them?

Hi Alison,
You might consider swapping your gravel for fine sand and making it a much thinner layer (1‐2 cm) which would enable your corys to do a better job as an eating controller for removing the larvae.

dw1305 wrote: ↑17 Dec 2020, 16:20 You can definitely reduce these by increased tank maintenance, they are very much associated with <"organic biofilms in damp situations">

To both of you, yes, water changes eliminated them repeatedly, but since staying up on water changes is my Achilles' heal, my kryptonite, they recur once or twice each year, mostly in summer months when humidity and temp rise together in the air gap below the tank hoods.

Again, a nuisance, but also a live food for my tetras and corys.

Cheers, Eric

Hi all,

bekateen wrote: ↑17 Dec 2020, 16:44.........To both of you, yes, water changes eliminated them repeatedly, but since staying up on water changes is my Achilles' heal, my kryptonite, they recur once or twice each year, mostly in summer months when humidity and temp rise together in the air gap below the tank hoods.

Again, a nuisance, but also a live food for my tetras and corys.......

I've learned to live with most of the uninvited guests in my tanks, trying to get rid of them usually causes more issues than leaving them.

I quarantine new fish (and treat if appropriate) and chemically treat Hydra if they get really bad, I hand pick Damselfly larvae, Snail Leeches and Planaria, but other than that I just let them get on with it.

cheers Darrel

Same here.

Cheers, Eric

Thanks to you both, I'm hoovering the gravel when I take out the regular couple of buckets.

It would be nice to have sand, but the Gibb (about 45cm total length now?, old photo) would disperse it everywhere.



The larvae are thin and brown and about 1cm long, they don't swim in any obvious way, they wave in the gravel like grass.

I'm glad that the fish aren't any actual danger though, I guess I'll just continue the slog to try and keep numbers down.

Is it just the lighting or is that a very strangely patterned gibbi?
-Shane

The lighting is quite yellow (camera rather than tank) but I don't think he's particularly unusually marked? I'll try and find another pic.

Shane wrote: ↑17 Dec 2020, 20:44 Is it just the lighting or is that a very strangely patterned gibbi?
-Shane

Apologies for the delay! I am lousy at tank photography, however...I think he is a standard pattern though.



My fly war continues...I have taken out half the gravel and am stirring the rest daily. The only good thing about lockdown is that no-one can see all the fly papers in my sitting room

Well, three months down the line nothing is improved, and certainly not my mental health. I hoover the gravel every couple of days to try and get rid of eggs and larvae (I don't want to do it every day because of having to take out water each time) and also hoover the walls above the tank to try and get rid of the flies. With a vacuum cleaner. The fish aren't happy, I don't know if this is because of me constantly disrupting them or the flies. There are far too many of them for the number and type of fish I have. I worry particularly about my Gibb, he's not eating as much as usual, but then he's 31 this year and could just be slowing down. It's always hard to know cause and effect in these things. If anyone has any other suggestions I would be delighted to try them. At the moment looking at my fish just depresses me. Should have stuck with mammals!