Who is the killer?

Tank = Juwel vision 260L. Running 6 months since refurb, recycle and restock.
Filter1 = Fluval 307 with Carbon - cleaned every 8 days.
Filter2 = Large air powered sponge filter - cleaned every 4 days.
Heater = 300w digital control.
CO2 Generator = DIY Citric/Bicarb regulated 2 bubbles / min. 8am-6pm.
Lighting = 24/7 planted phased led.
Autofeeder set for 0800 / 1200 / 1600 / 2000 daily.

Heavily planted.

Last water change 4 days ago - using gravel siphon.

Daily dosing with Flourish Advance. (Underdosed, and my other 3 tanks have all been run the same with the same water perameters)

Temp = 26 C
Ph=7.25
GH= 100mg/L
KH= 80mg/L
Nitrate = 0
Nitrite = 0
Ammonia = 0
TDS= 400ppm
Copper = 0ppm
Co2 = 15ppm

Red honey dwarf gourami x 6
Green Neon Tetra x 15
Lampeye Killifish x 15
Corydora Hasborus x 6
Dwarf Pleco x 2
Red Ramshorn snails x 20
Trumpet snails x 20
Blue Velvet Cherry Shrimp x 40

At 0430 yesterday morning, my son checked the tank and all was well. The lights had just switched on 'dawn' colours and everyone was doing what they normally do.

At 0730, I came downstairs to find 12 of the Green Neon Tetras dead at the bottom of the tank and the remaining 3 were swimming slowly at the bottom too.

All other fish / shrimps / snails were fine, doing what they normally do.

No sprays / cleaning fluids / etc have been used in the vicinity. (it's in the hallway).

I did an immediate 20% water change and put new carbon in the filter. Water tests showed all perameters fine.

Nobody but the Green Neon Tetras were affected.

I have attached a photo of the tank. (The white panels are moss walls installed 3 weeks ago).

Videos of the tank are here:


My question is... WHO KILLED MY NEONS!!!!?

 

Don't ask who, but what.

How long have you had the neons?

Also some other questions:
- Seems like you have quite a current in the tank, do I see that right?
- Do you always filter with carbon? (which is longterm not advisable)
- What is your maintenance regimen?
- What do you feed and why with an auto-feeder? And why 4 times a day?

Sidenotes:
a) This tank is not heavily planted. Believe it or not.
b) Pretty open in the upper regions, wondering if the gourami show signs of stress.

 

Don't ask who, but what.

How long have you had the neons?

Also some other questions:
- Seems like you have quite a current in the tank, do I see that right?
- Do you always filter with carbon? (which is longterm not advisable)
- What is your maintenance regimen?
- What do you feed and why with an auto-feeder? And why 4 times a day?

Sidenotes:
a) This tank is not heavily planted. Believe it or not.
b) Pretty open in the upper regions, wondering if the gourami show signs of stress.

Hi there,

Thanks for prompt help.

Neons have been in the tank for 8/9/10 weeks. (5 at a time).
Yes, the tank has a good current. the fluval is set to run the flow around the front, right to left.
Carbon is used two-weeks on / two weeks off, and when there's any additional need. (I dont use chemicals to treat disease in this tank. I use a hospital tank.
Maintenence is basically a gravel siphoned 20% water change every 4 days, using seachem prime. Filter clean every 8 days. Plants trimmed and trimmings replanted as and when they reach 3/4 tank height.
I use an auto-feeder as i'm very forgetful. 4 little feeds per day also stops them all getting stressy around a large single feed per day.
By heavily planted, I mean that most of the tank floor is covered with rocks / plants. I get that they're still not fully heavy.
As for the gourami, as far as I can tell, two of them are male and they have a spat now and again, but otherwise they are very placid and come and meet me at the glass whenever I approach.

I have a theory about what's happened, but I'm waiting to see if anyone else comes up with it.

 

Allright.

Yes, the tank has a good current. the fluval is set to run the flow around the front, right to left.

Tune it down. None of the fish species you have needs a current as I could observe in the videos. They don't come from standing waters, but much, much less curent.

Carbon is used two-weeks on / two weeks off, and when there's any additional need. (I dont use chemicals to treat disease in this tank. I use a hospital tank.

Using carbon except to remove meds is not necessary, actually even detrimental to the biological balance, as carbon filters indiscriminately and thus also stubstances that are beneficial are removed.

A hospital tank is not always a good idea, depending on what you have to treat. Some things have to be treated in the main tank due to their contagiousness. Any previous disease outbreaks?

Maintenence is basically a gravel siphoned 20% water change every 4 days, using seachem prime. Filter clean every 8 days. Plants trimmed and trimmings replanted as and when they reach 3/4 tank height.

Stop gravel vacuuming, that way you remove beneficial bacteria.
Instead of 20% waterchange every 4 days, do 50% every 7 days. Too small waterchanges don't dilute wasteproducts enough. Even if it mathematically adds up to 40% a week, it leaves out that more waste products are produced in the mean time.
Do you have chlorinated tapwater? If not, you can stop using a waterconditioner.
Filter cleaning also removes a lot of beneficial bacteria. A filter should only be cleaned when it starts to clogg. I only clean the pump of my filter every 2-3 weeks and leave the filtermedia untouched.
Let the plants grow up to the top the gourami will definitely appreciate it.

I use an auto-feeder as i'm very forgetful. 4 little feeds per day also stops them all getting stressy around a large single feed per day.

Fish are not stressed from feeding. Far from it. Also feeding time is when you should look if everybody is still there, healthy and eating. 2x a day the amount the fish eat in 2-5 minutes is absolutely enough. Also when you feed yourself you can make sure everybody gets enough. With your stocking it could be the Corydoras (which are still quite young) don't get enough food. Same could be for the neons. The gourami and lampeyes are mostly at the top, meaning they also get most of the food.

The question is still open: What do you feed?

By heavily planted, I mean that most of the tank floor is covered with rocks / plants. I get that they're still not fully heavy.

Heavily planted is when you see more green than anything in a tank.

As for the gourami, as far as I can tell, two of them are male and they have a spat now and again, but otherwise they are very placid and come and meet me at the glass whenever I approach.

Just try some cover from above with floating plants (remember to slow down the current) you will see more natural behaviour. To me it actually sounds a bit like they're overfed.

All in all, I see a massive problem with maintenance and interpretation of fish behaviour and health.
Also generally the tank looks too bright. Most fish like some shade.

My thought is, the neons might have been very stressed, half starved and perhaps one of the batches has brought in a neon-specific strain of a disease or parasite.

I've given you a number of hints and tipps. Hope it helps.

 

I agree that your tank is not heavily planted. I believe your main problem is too much flow in the water!

I have kept Green Neon Tetras for many years. If damselfly nymphs had not killed most the fish (Chili Rasboras and Tengahs), my Tetras would most likely all still be alive. But only one survived after I finally succeeded in ridding the tank of the damsel fly nymphs. That Green Neon Tetra, named "Fishy", is now over 5 1/2 years old!

These are "Black water" fish, as are Gouramis. That's the way I keep the aquarium. The darkness calms them and then they thrive, lose shyness and also develop their brightest colors! So here's my set up:

Dennerle diamond black shrimp gravel (that's with rounded edges, so it doesn't hurt fish or catfish/bottom feeders).
Catappa leaves to tint the water, help maintain a lower pH (although mine can manage fine with pH 7 - 7.5!)

Simple sponge filter with the attached diffuser set very low, for a bare minimum of surface aeration and water movement. It is pointed at a side wall so it doesn't bother the fish. In your videos, it is obvious to me that they can't manage the water flow.

Temperature kept at 26 - 27 C

Very dim lighting! In Fishy's aquarium, I actually stopped using lights several years ago. The aquarium is not too far from a window and I open the curtain in the early morning and keep it that way for a few hours, then close it. These times are when Fishy most often comes out of hiding and swims around. He is hand tame and also recognizes me and swims to the glass when I'm nearby.

I have some caves for him where he likes to hide out, probably due to light or just his pattern of activity.

Plants: only very low-light Cryptocornes.

Feeding: very fine "Nano" food or tiny amount of frozen white mosquito -- but I rarely feed that, as it is hard to dose and I don't want to pollute the tank. I feed him once in the morning every 3 days. Yes, you read that right! Because you have a group, you can feed them ONCE every day, but then a really tiny amount. You may think they are hungry, but they can actually live for a week without food.

My practices are probably considered controversial, but here goes: I only vacuum the bottom of the tank once or twice a year! I firmly believe that the debris that collects hosts many beneficial micro-organisms. (On light-colored gravel, it would be very noticable.) Green Neon Tetras have small mouths and do very well with eating copepods and other tiny critters that we can't even see.

The only thing I add to my water is Prime during water changes. I rinse out the sponge filter for Fishy once every two months in a pail of tank water. If he were still sharing the tank with his school of fish, I would rinse the filter once a month.
(He's moving to another tank this week and will have other companion fish and shrimp).

My advice: if possible, give your fish a Black water habitat, especially the dark gravel. If you won't do that, at least provide lots of shade with floating plants and caves to hide in. Use a minimum amount of water flow. Do not feed so much and so often. Get rid of the carbon filter. (I hope that you only rinse using tank water, not clean tap water!) Are those rocks aquarium-safe? If getting new Green Neon Tetras, try to get wild-caught ones. Mine were all wild-caught and I believe they are stronger.

The shrimp, Gouramis and Green Neon Tetras are fine together. I'll leave it to others to comment as to whether the other fish in your aquarium do well in the same conditions.

Best wishes!

 

Guys,

I really appreciate the hints and tips. I will make appropriate changes to the maintenance & feeding regime.

In answer to some of the points, I have always used a mixture of several foods (Aquarian / Herons / dried bloodworm pellets / etc), which I powder in a pestle and mortar. Some floats, some slowly sinks so that every mouth gets a go. It's worked for me for 40 years but I'm not averse to changing in if there are better suggestions. The four feeds per day are very tiny (about a 1/8 teaspoon each). This still maybe too much and I'll cut it back to two/day for now.

Yes, I use prime in water changes and use part distilled water to keep the TDS at around 400ppm as I live in a hard water area.

Lighting in use is a 24/7 LED timed unit which simulates natural lighting from dawn unitl dusk. It is much dimmer than the standard lights and really does show the colours from mid afternoon onwards. (I had it on max to take the videos).

Apart from using a dense pre-filter on the fluval 307 intake (which I'm not keen on as it clogs very quickly), do you have any other suggestions as to how to reduce the flow without putting undue strain on the motor/impeller?

Yes, the rocks are aquarium safe. They are slightly above normal in carbonate to help the invertebrates but, again, I've never had cause for concern with these.

I hadnt considered the floating plants idea. The aquarium has always had plants from floor to ceiling but, since refurbishment six months ago, I have concentrated on pruning and replanting cuttings to bush them out. (Every plant you see came from 1 or 2 stems of each type.) I guess now is the time to leave them be and let them reach the top. In the meantime, I'll get some floating plants.

All good advice guys and I'm very grateful.

However, what is really bothering me is that this was 'an event'. Something happened suddenly in the tank to cause all the neons, and no other fish, to drop dead all at the same time.

My thoughts were, and still are, that some sort of toxin got into the water and obviously affected the neons more than others.

Going down this line of thought, I changed out the carbon for new and doubled the size of the carbon bag in the top media tray of the filter yesterday. This was done in the hope of removing whatever toxin was in the water.

This morning, the remaining 4 neons are back up in the mid-water happilly trying to shoal. This leads me to believe that there was, indeed, a toxin in the water which has now been cleared by the carbon.

The question remains - 'what was the toxin and where did it come from?'

No sprays, cleaners, polishes, etc have ever been used near the tank, and yesterday was no exception. So the toxin must have originated inside the tank.

Picking up on what MacZ pointed out, it could have been that the corydoras may have not been getting enough food. When corydoras get stressed, they are know to release a toxin into the water. (There are plenty of stories of corys killing themselves with it on the way home from the aquarium shops.)

So, my theory is that, for some reason, be it hunger or otherwise, something stressed the corys and trigged their toxin release. The neons being the most sensitive, copped a gill-full of it and promptly croaked.

What say you?

 

Guys,

I really appreciate the hints and tips. I will make appropriate changes to the maintenance & feeding regime.

In answer to some of the points, I have always used a mixture of several foods (Aquarian / Herons / dried bloodworm pellets / etc), which I powder in a pestle and mortar. Some floats, some slowly sinks so that every mouth gets a go. It's worked for me for 40 years but I'm not averse to changing in if there are better suggestions. The four feeds per day are very tiny (about a 1/8 teaspoon each). This still maybe too much and I'll cut it back to two/day for now.

Yes, I use prime in water changes and use part distilled water to keep the TDS at around 400ppm as I live in a hard water area.

Lighting in use is a 24/7 LED timed unit which simulates natural lighting from dawn unitl dusk. It is much dimmer than the standard lights and really does show the colours from mid afternoon onwards. (I had it on max to take the videos).

Apart from using a dense pre-filter on the fluval 307 intake (which I'm not keen on as it clogs very quickly), do you have any other suggestions as to how to reduce the flow without putting undue strain on the motor/impeller?

Yes, the rocks are aquarium safe. They are slightly above normal in carbonate to help the invertebrates but, again, I've never had cause for concern with these.

I hadnt considered the floating plants idea. The aquarium has always had plants from floor to ceiling but, since refurbishment six months ago, I have concentrated on pruning and replanting cuttings to bush them out. (Every plant you see came from 1 or 2 stems of each type.) I guess now is the time to leave them be and let them reach the top. In the meantime, I'll get some floating plants.

All good advice guys and I'm very grateful.

However, what is really bothering me is that this was 'an event'. Something happened suddenly in the tank to cause all the neons, and no other fish, to drop dead all at the same time.

My thoughts were, and still are, that some sort of toxin got into the water and obviously affected the neons more than others.

Going down this line of thought, I changed out the carbon for new and doubled the size of the carbon bag in the top media tray of the filter yesterday. This was done in the hope of removing whatever toxin was in the water.

This morning, the remaining 4 neons are back up in the mid-water happilly trying to shoal. This leads me to believe that there was, indeed, a toxin in the water which has now been cleared by the carbon.

The question remains - 'what was the toxin and where did it come from?'

No sprays, cleaners, polishes, etc have ever been used near the tank, and yesterday was no exception. So the toxin must have originated inside the tank.

Picking up on what MacZ pointed out, it could have been that the corydoras may have not been getting enough food. When corydoras get stressed, they are know to release a toxin into the water. (There are plenty of stories of corys killing themselves with it on the way home from the aquarium shops.)

So, my theory is that, for some reason, be it hunger or otherwise, something stressed the corys and trigged their toxin release. The neons being the most sensitive, copped a gill-full of it and promptly croaked.

What say you?

Not sure on what happened to the neons or your theory, but it certainly sounds strange whatever has happened.

However, to reduce the strength of the flow of your filter you could use a spray bar instead of the standard output nozzle. Fluval do a spraybar kit compatible with the 307 which you can pick up off amazon quite easily.

 

My thoughts were, and still are, that some sort of toxin got into the water and obviously affected the neons more than others.

Picking up on what MacZ pointed out, it could have been that the corydoras may have not been getting enough food. When corydoras get stressed, they are know to release a toxin into the water. (There are plenty of stories of corys killing themselves with it on the way home from the aquarium shops.)

Before anything else: No, sorry, the theory doesn't work out. If that was actually the case, a lot of people would report problems with Corydoras after transport. The only species the in-bag-death due to toxin are documented of are Corydoras (former Brochis) splendens and Corydoras sterbai and it was after shipping from South America to North America and Europe. So the animals were in a much smaller volume of water and for several days with no filtration. DoubleDutch (our resident Cory specialist) will know more about this.
Corydoras habrosus are definitely not known to be poisonous.

And generally if it was a toxin all fish species would be affected, not only one species.

I may have answers as to why the species might not do well in your tank, but not at all why they all died at once.

But in the end: Why exactly they died might stay a mistery. It's often hard to tell the cause of death in hindsight anyway, but especially when the owner can't offer much info in terms of observation.

 

However, to reduce the strength of the flow of your filter you could use a spray bar instead of the standard output nozzle. Fluval do a spraybar kit compatible with the 307 which you can pick up off amazon quite easily.

I don't find it difficult to position and direct the standard Fluval outlet in a manner that achieves the flow and circulation that I want. I'd just encourage the OP to experiment a bit using the tank walls as baffles. I've never had to reduce the flow rate at the filter. Alternatively a spray bar is certainly an option. Denser planting and strategically placed driftwood can also reduce the flow.

 

My diffuser came with the sponge filter and has a knob to adjust the flow. I can have it produce a strong flow with many fine bubbles, or a gentle flow where you just see the plants moving or anything in between. It's an Aquael Mini-Pat Sponge filter. I have used these filters for years and have a small supply for future tanks.

 

Guy’s,

OP indicates water parameters all read 0?

 

All very good advice provided. IMO, the sudden Neon kill was due to their sensitivity to unstable water conditions. The over cleaning of filter media, the use of carbon, maybe even overdosing the plant fertilizer a bit. The fact the nitrate level is zero is concerning, might indicate a cycling problem.
Very pretty tank. Maybe overdoing things a bit.

 

Guy’s,

OP indicates water parameters all read 0?

Yes, coming definitely from using carbon.

Edit: And cutting with distilled water.

 

Morning all,

I have installed the fluval diffuser bar and the tank is realy calm now. Nobody is struggling to stay in one place!

I have done a bit of research with regards to toxin release from Corydora Hasboras and it definitley is a thing. Have a look at this link:

Self-Poisoning: A Damaging Defense Mechanism | RateMyFishTank.com

I also spent an hour in conversation with staff at my LFS. They have come accross this a few times with their costomer's tanks. They also state that, if a supplier sends corys together in one big bag, they arrive dead and are struck from their approved list. The good suppliers will send their corys in bags of five, with heat pads, sponges in the water to provide baffling, pure oxygen filled bags, additional packaging in the box, etc, the works. They dont get many arrive dead at all but, on the odd occasion that they do, the entire bag of five will have succumbed.

 

The article names peppered corydoras, which are Corydoras paleatus. Habrosus have the common name of salt-and-pepper-corydoras.
It is still a different situation if you have hundreds of liters or a small bag. It's extremely unlikely to have happened in your tank. But if you want to believe it to be the reason, your choice.

 

Morning all,

I have installed the fluval diffuser bar and the tank is realy calm now. Nobody is struggling to stay in one place!

I have done a bit of research with regards to toxin release from Corydora Hasboras and it definitley is a thing. Have a look at this link:

Self-Poisoning: A Damaging Defense Mechanism | RateMyFishTank.com

I also spent an hour in conversation with staff at my LFS. They have come accross this a few times with their costomer's tanks. They also state that, if a supplier sends corys together in one big bag, they arrive dead and are struck from their approved list. The good suppliers will send their corys in bags of five, with heat pads, sponges in the water to provide baffling, pure oxygen filled bags, additional packaging in the box, etc, the works. They dont get many arrive dead at all but, on the odd occasion that they do, the entire bag of five will have succumbed.

It's clear to me that you want the best for your fish. I'm glad you've got a calm water flow now. Are you removing the carbon filter? Do you plan to try Green Neon Tetras again in the future?

 

Morning all,

I have installed the fluval diffuser bar and the tank is realy calm now. Nobody is struggling to stay in one place!

I have done a bit of research with regards to toxin release from Corydora Hasboras and it definitley is a thing. Have a look at this link:

Self-Poisoning: A Damaging Defense Mechanism | RateMyFishTank.com

I also spent an hour in conversation with staff at my LFS. They have come accross this a few times with their costomer's tanks. They also state that, if a supplier sends corys together in one big bag, they arrive dead and are struck from their approved list. The good suppliers will send their corys in bags of five, with heat pads, sponges in the water to provide baffling, pure oxygen filled bags, additional packaging in the box, etc, the works. They dont get many arrive dead at all but, on the odd occasion that they do, the entire bag of five will have succumbed.

I have heard of this before, I don’t know much about it, it is interesting, but the release of toxins would be a defense mechanism in response to stress (such as a potential predator or being captured and stuck in a small bag). I doubt very much they would be sufficiently stressed in an aquarium just because of lack of food. I have also heard of dwarf gouramis attacking neon tetras, but in that case they would be bitten and would be killed off gradually not all at once. The most likely explanation is that suggested by A201, the neons perhaps being more sensitive than the other fish.

 

It's clear to me that you want the best for your fish. I'm glad you've got a calm water flow now. Are you removing the carbon filter? Do you plan to try Green Neon Tetras again in the future?

I have had a chat with a friend's daughter who is a marine biologist. She agreed that there is a risk that the corys released a toxin into the water. She has seen corys die suddenly at aquariums she has worked at and it has been observed in the lab during frenetic mating in more than one type. She noted that my ph was at the upper end of the hasbora tolerance range and over the GNT tolerance range. She also said that commercially tank-bred fish can develop genetic weaknesses due to excessive inbreeding and might explain why the tetras were the only ones affected. She advised to keep the carbon in the filter for a couple of days to remove any trace of the toxin and then to ad more almond leaves to lower the ph to 6.5; and to keep observing the corys to try and establish the male/female ratio as that may also be an issue.

Catappa: in answer to your question, I have four surviving GNTs and will wait for things to settle before replacing those lost.

 

If you are able to obtain wild-caught GNTs, they are much hardier.

 

If you are able to obtain wild-caught GNTs, they are much hardier.

I heard that. How do I find out if they are endangered / protected? Wouldnt want to be part of anything like that.

 

and then to ad more almond leaves to lower the ph to 6.5;

Do you know your KH? Leaves and other botanicals only impact pH significantly when the KH is below 1°.
You already said you use distilled water, lowering the KH with it is going to be expensive longterm, so maybe an RO unit would be a good investment.

 

Do you know your KH? Leaves and other botanicals only impact pH significantly when the KH is below 1°.
You already said you use distilled water, lowering the KH with it is going to be expensive longterm, so maybe an RO unit would be a good investment.

Kh is 7 and has been steady for a while. I only use 6l of distilled water on each change, just to keep the kh from going too high, My landlord wont let me intall an RO unit.

 

With that KH leaves and alder cones will only tint the water and have no further effect than maybe 0.2 pH-points downward for maybe a week.
An RO unit doesn't have to be fixed to the faucet. There are more than enough you only screw on the tap with an adapter.

 

I heard that. How do I find out if they are endangered / protected? Wouldnt want to be part of anything like that.

They are not endangered. I checked the 2021 red list from the IUCN.