A strange cycle of behavior and death in peppered corydoras

[Lancerguy]

Tank

What is the water volume of the tank: 20 gallons

How long has the tank been running: Just under 6 months

Does it have a filter: Aquaeon quietflow 20

Does it have a heater: Yes

What is the water temperature: 78 degrees

What is the entire stocking of this tank: 11 Neon green rasboras, 8 corydoras (at time incident began, only 6 currently)

Maintenance
How often do you change the water: weekly

How much of the water do you change 30%, following the guidelines of the AqAdvisor app.

What do you use to treat your water: I have stress coat + which is my primary conditioner, seachem prime on hand in case ammonia is detected in water.

Do you vacuum the substrate or just the water: I vaccuum the substrate

*Parameters - Very Important
Did you cycle your tank before adding fish: I thought I had, but quickly learned I hadn't. By the time the incident I'm reporting began, my tank had cycled, however.

What do you use to test the water: API master test kit

What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.

Ammonia: 0.00 as of this week (0.25-0.50 when incident first began)

Nitrite:0.00

Nitrate:Less than 5 PPM

pH:6.8

Feeding
How often do you feed your fish: 6 days a week

How much do you feed your fish: A pinch of flake food, alternating sinking tablets twice a week

What brand of food do you feed your fish: Tetra tropical flakes and bloodworms, Fluval bug-bites, Aquaeon bottom feeder tablets

Do you feed frozen or freeze-dried foods: Frozen baby brine shrimp once a week

Illness & Symptoms
How long have you had this fish: Corydoras have been in my tank for just over 3 months now

How long ago did you first notice these symptoms: 10 days

In a few words, can you explain the symptoms: It starts with one of the corydoras spending their down time hovering at the waterline instead of resting on the substrate. Other than this, they behave normally, but gradually grow weaker over the next few days, and eventually die. Only after the original suffering corydora has died does another one exhibit this trait. I've never had two behave in this way at the same time.

Have you started any treatment for the illness: I wasn't sure it was an illness until the second corydora began to behave strangely, now trying to deduce what treatment would be best.

Was your fish physically ill or injured upon purchase: No

How has its behavior and appearance changed, if at all: The only change to their behavior is listed above. They still congregate with their fellows, demonstrate normal appetite, but strength of swimming slowly declines.

Explain your emergency situation in detail: A couple months ago, I decided to upgrade my filter to accomodate the greater population in my tank, not thinking about how doing so would wreck the microbiome of my tank. My water parameters remained stable for a while longer, but two weeks ago I discovered an ammonia spike in my tank. I caught it early, hovering around no more than half a part per million, and around this time the first Corydora was displaying the behavior outlined above.

I did 30% water changes every 48 hours for the rest of that week, and returned the ammonia level to 0, but by the end of that first week I had my first casualty. At the time I pondered whether the ammonia had killed him, but he was the only fish in the entire tank to change his behavior, so my working theory was that stress from the increase in ammonia had caused him to succumb to some kind of disease or parasite.

Later the same day the first one died, a second one had already adopted his strange behavior. I tracked the water chemistry to make sure I was keeping the ammonia under control, hoping that the improved conditions might help him recover, but a few days later he died, as well.

After that, 48 hours passed, and I thought perhaps the nightmare was over... but I got home from work tonight to discover that a third Corydora has begun to hover at the waterline. Now, I know that this won't stop just because I've stabilized the water, and I'm trying to figure out what step I should take next.

 

[tomiyama]

Hello there, I had a similar experience with a youngish tank 10 years ago, corycats are extremely sensitive to ammonia/nitrite levels and really needs a well-established aquarium. I lost several because by good bacteria were not built up enough in my tank, and even though I couldn't detect ammonia/nitrite in my tank, there must have been trace amounts and before they died, they were constantly gasping for air at the surface.
I would stop feeding them for at least a few days and perform daily water changes but do NOT vacuum the gravel/remove your filter which houses lots of good bacteria for at least 3 months as you will remove too much of the beneficial bacteria.
Do you have any corycats left or did they all die? I feel for you, it's a horrible feeling. I waited until my aquariums was at least 9 months old before I bought any more corycats, and I haven't had any problems since.

 

[tomiyama]

Oh and I forgot to add that the trace ammonia/nitrite levels directly cause the corycats to suffocate and die as they can't get enough oxygen into their system, I'm pretty sure that's what is happening to them....

 

[DoubleDutch]

Do you feed the tablete two times a week or alternate two times a week ?

In case of the first, feed them (meaty) tablets every day. A pinch of flakes isn't enough and noticed that especially Tetra flakes often occure in issuethreads.

 

[Fisch]

Do you feed the tablete two times a week or alternate two times a week ?

In case of the first, feed them (meaty) tablets every day. A pinch of flakes isn't enough and noticed that especially Tetra flakes often occure in issuethreads.

I agree, it sounds like they could use a bit more Cory specific food.

 

[DoubleDutch]

Has the watertemperature been constant 78F?

 

[Lancerguy]

Hi all, sorry for the delay in reply. My answers to the questions posed are as follows:

1.) Of the 8 cory cats I started with, I still have 6. The one who started hovering near the surface the day I posted this message is still alive, as of this reply. He's lived the longest of the three so far who have had this happen, though the behavior hasn't corrected itself.

2.) I should specify a bit about the hovering: while they remain close to the surface, they don't appear to be gasping. Their mouths aren't breaching the surface of the water they just... hang there. It's sort of like how they normally chill on the substrate when they aren't eating or socializing... just up near the top of the tank instead.

3.) I've considered that it might be an issue with exposure to ammonia/nitrites/nitrates when I screwed up my microbiome... I guess the reason I'm still debating that is that they seem to be reacting to it one at a time. If it were an issue with with ammonia, wouldn't they all be displaying symptoms at the same time? I initially thought it was some kind of parasite who took advantage of stress compromising their immune systems... but I've been doing research nonstop since this started and I can't find any diseases/parasites that would cause the behavior I'm witnessing.

4.) I feed the tablets 4 times a week. my feeding schedule generally goes:
Su.) flake food/sinker pellet
M.) bloodworms
T.) bug bites/ algae pellet
W.) frozen brine shrimp
Th.) Flake food/ sinker pellet
F.) Bloodworms/ algae pellet
Sa.) Fast day

The days alternate, but the arrangement of feeding doesn't. Should I be dropping more pellets?

Thank you for your suggestions though! I haven't stopped the water changes, though I had been gravel vacuuming. I was worried if I didn't ammonia would build up too fast. Will the Cories be okay if I go a few months without vaccuuming? There tends to be a lot of gunk even when I just wait a week. How many days is it safe to go between feedings?

A few days ago I realized my ammonia readings were stuck at .25 PPM, and remained that way no matter what I did, so I think I'm still struggling to stabilize my microbiome. I've started adding bottled bacteria to the tank, though I've heard it's not a super reliable method.

 

[Lancerguy]

Also, yes, the temp has remained consistently in the range of 76-78 degrees, throughout. I try to keep the water I use for water changes at room temperature so that the change it brings to water temperature is always the same.

Editing just to add an update: I think I may have at least discovered why they die after a few days of hovering at the top of the tank... I think my rasboras may be nipping their fins while they're up there. Victim number 3 took a turn for the worst this morning, and is unlikely to survive the day... his tailfin has been reduced to just a little nub.

I bought the neon green rasboras as my starting fish because they were tiny, hardy, and peaceful natured... and a few months later I added cories as my second species because I figured they could occupy their seperate stratas of the tank and just coexist... which was the case for the first few months... but I guess these are special circumstances.

 

[tomiyama]

I'm so impressed with your cories, they are super tough, most cories would die with a .25 ammonia reading, mine all died and I couldn't detct the trace amounts. I couldn't keep cories alive until my tank was 10 months old.
Personally, I still think it's the ammonia/nitrite as my cories didn't exhibit symptoms all at once, they would slowly succumb over the weeks one by one, and hovering near the top (which is abnormal for most cories) meaning that something is wrong. Some cories have a stronger detox/organ/immune system than others so that's why not all get sick & die at the same time.
Also, you are right, ammonia/nitrite is heavier than water so the concentrations are higher near the bottom, which is probably why they are hovering near the top too, they know it's less toxic near the top.
I would:
1) partial daily water changes like you've been doing, and instead of touching the gravel at all, just have the end of your gravel vac near the bottom. Beneficial bacteria only live on the surfaces of your aquarium, and having the "mulm" which may be unsightly is actually loaded with beneficial bacteria in a well-established aquarium which you won't have for a while yet. By removing the water near the bottom, that is where the highest concentration of toxins are, but by not touching the gravel and mulm, you do not remove any good bacteria which is critical right now.
2) Do not feed every day, fish can go several days without eating. I would definitely not do more than every 2-3 days at this point, and extremely small amounts (some fishkeepers say that assume their stomach is the size of their eye). Right now what's killing them is the ammonia level in your tank, and when it finally converts to nitrites, that is even more deadly before it converts to much safer nitrates. When fish are sick enough/near death, they won't eat anyway.
3) I would check ammonia and nitrite levels daily, and although I've never used bottled bacteria, it's worth a try in small amounts.
4) Sounds like you are handling it very well, with any luck your cories will survive while your tank is cycling, which unfortunately can take weeks.
Keep us posted, we are all in this together .

 

[DoubleDutch]

0,25 ammonia seems to be a minimum amd often a false reading.

Feed corys every day but replace the algaewafers by shrimppellets. Corys are.mainly carnivorious. Don't starve them.

The temperature is quite high for Peppers.
Can you lower the temp ?

 

[Lancerguy]

Alright, so, for an update today:

I went to bed last night fully expecting I would need to bury number 3 before I went to work that day. I was pleasantly surprised to find that, when I woke up, not only was he alive, but he was congregating with the other cories on the ground. He even showed some interest in food today. While I'm hopeful I can get this ammonia spike issue resolved in time to save the remaining 5 cories, I'm not letting myself get my hopes up that he, specifically, can be saved at this point... his tailfin is quite depleted,and he's lost a lot of color, but at least he's able to live normally for a while, and I guess that's the best I can hope for now.

I've decided to alter my treatment a bit based on the advice posted here. Instead of a 30% water change every 48 hours, I'm going to start doing a15-20% water change daily... I'll try to do it before the aquarium light kicks on, to minimize any extra stress the frequent water changes may cause.

Once my tank is established, how often should I vacuum my gravel? I was led to believe it should be a weekly thing, but I don't want to deplete my tank again.

When I first detected the ammonia, I started feeding my fish every other day instead of following my six-day program I'd used for the remaining four months I've had live fish in the tank. I'll test the water after changes and if the numbers don't improve I may go down to once every third day for a week or so.

As of today, the test results haven't changed: ammonia .25 PPM, nitrites 0 PPM, Nitrates more than zero and less than five.


As to the temperature of the tank, unfortunately I can't do a whole lot about lowering it at the moment, short of installing a cooler in the tank. I live in the pacific northwest... and while the upside to that is that summers here are very, *very* mild, the downside is that most residential areas, including mine, don't come with air conditioning. The temperature in my house is manageable for me, but tends to average near the mid-70s. I could turn my heater down, and when I read your message I did lower it down to 75... but realistically 75 is about as low as I'll be able to consistently keep the tank until the autumn weather hits... fortunately, that's only a few weeks away.

That said, I do a lot of digging around online before I add a species to my tank, and a big part of the reason why I picked peppers, specifically, is because most references I found said they had a higher temperature threshold than the other species, and could thrive as long as the water was lower than 80, especially if they were captive-bred, as mine are. I kept my tank at 78 simply because that seemed to be the temperature that other tropical fish prefer.

 

[tomiyama]

Sounds like a plan . When a person fishless cycles a tank they do not touch the gravel or the filter for the whole period, which is usually 1 to 2 months.... I would wait at least thAt long because your tank is going through a mini spike right now. And of course don’t touch or change the filter as it houses and grows your beneficial ammonia and nitrite eating bacteria.
Don’t worry mulm is actually good for your tank and cory fry for example like to bury themselves in it.
If the numbers don’t improve you could increase the percentage water change by another 5 to 10 percent as well, just be careful to dechlorinate and use the exact same temperature as the tank.
Your cories are lucky to have a diligent fish keeper like you!
Was also thinking to increase the oxygen levels in your tank you could insert a plug in air bubbler line into your aquarium as beneficial bacteria will grow faster with increased oxygen levels and circulation And also provide more oxygen for your fish with damaged or impaired gills....
I think I bought my plug in air bubbler for $30 plus tax at the store.

 

[Lancerguy]

Haha, well, I feel my cories would be luckier still to have had a keeper who had the forethought to realize completely changing filters halfway through cycling a tank would have some negative repercussions, but I'm certainly doing what I can to try to fix my mistake.

Number 3 finally succumbed to his injuries today. I examined his body after removing it from the tank, but much like the other two, there were no visible signs that indicated any sort of illness or injury, outside his dorsal and tailfins being nipped pretty badly. He survived six days from first displaying symptoms to death, which is the longest yet. I wonder if he may have been able to pull through if I'd managed to protect him from the rasboras... but I don't know how I would have even managed to do that.

After number 2 died, I had a period of 2 days before the third victim began exhibiting symptoms, so I'll be using that delay as a benchmark for whether conditions in my tank have improved.

Today's test results were the same as yesterday's. Today is also the day I applied the bottled bacteria, after my water change. I shopped around to try to find a product that at least had positive reviews for it, and settled on one called "Nite out II", designed to be used in conjunction with another product called "Nite Out Special Blend". My ammonia levels are only mildly elevated, so i figure my microbiome is close to being where it needs to be, and hope this will help bolster the populations a bit faster... if for no other reason than to justify using the products, which made my tank smell like hydrogen sulfide for hours afterward.

per the instructions of the bottles, I'll be keeping my UV lights off on the tank for today, which made observing the behavior of my remaining cories difficult. I was able to confirm all 5 are still alive though.

Outside this bacteria application, I'll be sticking to the plan I already outlined above, unless some new information comes to light. I'll update the thread if there's any change, positive or negative, or in one week.... whichever comes first.

 

[Lancerguy]

Happy one week later! So, happily, I haven't had any other issues with strange behavior or death for my cories... though I haven't managed to get a zero reading on my ammonia in the past week, either... to the point where I'm starting to wonder if it really is a false positive of some kind.

For the past week I've done water changes daily, and my cories have become more active in recent days, so I'm starting to let myself be cautiously optimistic that things are improving.

As per the instructions of the thread, I haven't been gravel vacumming, only drawing water from the bottom of the tank, and as such a lot of detritus has begun to accumulate within the substrate. I've also purchased a wider variety of protein-based sinking pellets.

I'm tempted to say that the situation is over, though I'll keep doing things on emergency routine like this for at least a little while longer. Had an unrelated scare earlier this week, when a random hot day hit the island-- granted it was 'Washington' hot... that is to say, low to mid 80s... but when you have no air conditioning and heat-sensitive fish, it was enough to cause a scare. My tank never climbed above 80 degrees, but I had to resort to turning off the light, taking off the lid, and running a fan over the water.

 

[tomiyama]

Way to go Lancerguy, how promising! Does that mean that the ammonia is still stuck at the same reading or is it going down a bit? The full cycle can take weeks so perhaps the bacteria are just trying to build up, and when you see the ammonia fall you can measure the nitrite which will start going up before it falls to zero (nitrite is toxic too).
Smart moves on the heat management, especially because peppered cories do not like the higher temperatures compared to other cories. So sorry about the fires, I live just north of the border and my eyes and throat are sore and even the air is a bit smoky here so it must be tough for you and your fish,

 

[mattgirl]

I am happy to hear that things seem to be improving. One recommendation I don't agree with is not vacuuming your substrate. Corys constantly dig through the substrate looking for food. I actually try to keep my substrate clean specifically for my corys. You are not removing bacteria or very little bacteria when pulling the detritus out of there. The bacteria is clinging to the gravel.

I also can't imagine an ammonia reading of .25 being deadly for your little guys. It is best to get a 0 reading but .25 isn't something to get overly concerned about. I certainly wouldn't be comfortable with anything any higher though.

I agree with DoubleDutch about the amount of food your little guys are getting. They are not vegitarians so need a meaty diet and need to be fed daily. I feed my corys shrimp pellets and wafers designed for bottom feeders including corys. I also make sure some of the flakes or crisps I feed all my other fish make it to the bottom for my corys.

Once a week they get either freeze dried blood or tubifex worms. It is difficult to get this food down to them but I soak it in some tank water and pour it into the tank quickly. By doing so lots of it gets to the bottom before the other fish get all of it. My normal bottom sitting corys will come up mid-tank for this meal.

I do have to wonder if your filter is big enough for this tank. Sadly manufacturers over rate the effectiveness of their filters. You may want to consider getting a much bigger filter for this tank. You should be able to move the media from this filter to a bigger one without it having an affect on your cycle. A bigger filter with more media will add more area for your bacteria to grow on.

I actually run a filter designed for a 20 gallon tank on my 5.5 gallon tank. I've even gone way overboard on my pleco grow out tank and run a filter designed for a 55/100 gallon tank on it and it is only 12 gallons. You can never over filter a tank. There can be too much water movement but never too much filtration. The water movement can be baffled.

 

[tomiyama]

Good point matt girl perhaps mulm is only highly beneficial in well-established aquariums with a reading of 0.
I think a good compromise would be to "lightly" run the siphon over the substrate to remove excess mulm and debris and yet be careful not to disturb the gravel below where the good bacteria are trying to grow and get established. This way the beneficial bacteria growing on the gravel are not sucked up and removed.
I guess I love mulm because it's so cute when my corycat fry were little they would bury themselves in it with only their eyeballs showing it was adorable. Plus they seemed to eat whatever beneficial organisms were in the mulm, but again, I have a well-established 45 g....

 

[Pfrozen]

It sounds like the issues have been resolved so hopefully I'm not highjacking the thread by asking this!! Someone mentioned tetra color flakes not being a good source of nutrition is that right? I use that product and notice my fish act hungry even after i feed them

 

[Lancerguy]

Tomiyama: Yeah, basically, for the past week and some change, every time I test for ammonia, the color always comes out yellow-green, but more green than yellow. The implication is that it's constantly at or just below .25 PPM. It's possible it's a false positive, but since I was able to get fully yellow readings not long ago, I suspect there's some unseen source leaking trace amounts of ammonia into my water. My plants are all green and thriving, so I'm not sure what it could be, though.

To be safe, I've been considering putting ammonia neutralizer into the tank daily, but I fear that may slow the nitrogen cycle down.

Mattgirl: I've seen that mulm is a controversial element of fishkeeping ever since this whole thing happened, with a lot of voices for and against it. I'm not experienced enough to know which to believe, so for now I'll just compromise on it and see how my fish react. I knew from the start I would be adding cories to the tank eventually, so I added an extra half inch to the recommended substrate depth when I was setting the tank up. For now I'll vaccuum the top half of the gravel, and leave the mulm that settles in the deeper parts.

With regard to the filter, I've considered whether it was powerful enough for the tank, as well. However, since I didn't even have the foresight to transplant media from my old filter into the new one, it had to start its cycling from scratch, and it hasn't quite been 2 months since I made the switch. I'll see if I'm still struggling to balance my tank by the end of this month and decide what I want to do with the filter from there.

My one concern with a stronger filter is that even the current 20 gallon filter causes so much pull that I needed to dampen the intake with a sponge for my tiny neon greens to swim without dipping. I'm contemplating reorganizing my plants, since I've heard that having plants/decorations more centered in the tank can dampen the pull of the filter, too. I originally arranged the tank so that there would be an empty space in the middle, with plants and decorations forming an half circle around it, so the cories would have a place in the tank they could go if they were feeling stressed and wanted to feel hidden.


Pfrozen: I'm not nearly experienced enough to give an informed opinion, but over the months I've gradually increased the foods I rotate... and now have 4 different flake/floating foods, 4 different sinking foods, and 2 different frozen foods. I don't know that I've observed my fish acting more hungry after tetra flakes than any other food, though they're not the food that makes them the most excited to eat, either.

 

[Lancerguy]

Hmm... my cories are fine, basically back to their old selves... but I came home from work today to find that 3 of my neon greens had died over the span of one night. I'm not sure what could have caused it. They've been fine this entire time, I haven't had issues since I added them to my tank five months ago... Well, I'll need more information before I can deduce anything. their behavior hasn't changed any at all.

 

[DoubleDutch]

Hmm... my cories are fine, basically back to their old selves... but I came home from work today to find that 3 of my neon greens had died over the span of one night. I'm not sure what could have caused it. They've been fine this entire time, I haven't had issues since I added them to my tank five months ago... Well, I'll need more information before I can deduce anything. their behavior hasn't changed any at all.

Mmmmmm that's weird.

 

[tomiyama]

Ditto, very odd.
Did you check the temp of your tank? And when you added the new water, did you remember to dechlorinate it with the dechlorinator. swish it around in the bucket, and check that it was the same temperature as your tank?

 

[Lancerguy]

I'm pondering a few possibilities... though the only way I'll be able to know for sure is if more die, so hopefully I can't find out for sure.

Failure to dechlorinate feels unlikely, since I always dechlorinate water a day before adding it to the tank, but just to be safe I added more water conditioner to the tank. One of the three was stuck to my filter in a very awkward position... a place where his body wouldn't have naturally drifted if it got caught in the flow post-mortem. The dampening sponge had slipped down a little bit, so the top of it was uncovered, I think he may have tried to pass behind the fiter in the night and gotten trapped.

I don't thinkthis comes down to water quality, at least. Neon Greens are hardy little guys who weathered the ammonia spike that killed 3 of my cories without even altering their behavior/appetite...I can't imagine ammonia or nitrate would have gotten bad enough to kill them without doing worse to my cories... especially with me doing daily water checks and changes due to the emergency I *just* resolved.

The other thing I'm worried it could have been is that they may have tried to ingest some debris. When they aren't shoaling, my neon greens like to either dart about the middle of the tank or hang out with the cories at the bottom. They tend to try to eat any vaguely food-looking thing that crosses their path, and a couple times over the half year I've been doing this I've caught individual strands of dog hair in the water column, which I've promptly removed out of fear they may try to eat it and gum their digestions up. I haven't seen any such items in the water lately, so this is just me being paranoid.

Temp is 75. I lowered it for the comfort of my cories last week. It was at 78. Heater is working fine.

I resolve one emergency and another one crops up! Hopefully this was just a one-time tragedy.

Thanks as always for your help though, everyone. I had everything going so well for so long... this has been such a bad month for my poor little guys.

 

[Lancerguy]

One (hopefully) final update to the saga of my tank, now that enough time has passed and everything has been consistent enough that I'm... perhaps optimistically... finally beginning to hope that I've finally fixed this issue.

I've come to the conclusion that the three dead neons were an unrelated tragedy. Perhaps they got caught in the exposed filter uptake while eating the sinking pellets, perhaps I didn't sufficiently condition some of the small amounts of water I was using for a water change one day and the younger of the school were affected by it. Either way, it hasn't repeated itself.

Likewise, my cories are fine and my water conditions have been stable. I think my biofilter is finally starting to normalize after an intensely stressful month. If trends continue I'll start to gradually reduce my water changes until it's back to a weekly thing, and life can finally return to normal.

The only thing that's changed recently is that I've begun to fully vacuum the gravel again. I wanted to test for myself whether mulm would benefit my cories or not, but an outside factor made the decision for me: This weird slimy, tentacle-like algae EXPLODED into my tank. Like, over the course of two days it grew to just... just cover everything. I've never seen it before, and since the detritus at the bottom of my tank was the only change to my upkeep, I need to eliminate it as the possible cause before moving on to anything else.

Thanks for all your help, guys! I feel like I learned a lot, I just with 3 cories didn't have to die for me to do it.