Sudden tank deaths

[larochem595]

So here's what I do know--the primary symptoms are inflamed gills, heavy pumping of gills, darting/flashing, eventually bloating and death (in the end stages.) I know that heavy water changes and thorough gravel vacuuming certainly haven't hurt (possibly help a very small bit), but hasn't been a cure. I am doing two 20% water changes a week at this point. I know this tank is not overstocked and, other than a lower KH than I ideally want, the water parameters are spot on. The care I give them is good. I am pre filtering through carbon and pre-aerating my water. I also know that this started after the addition of new fish, which also leads me to believe it is an infection of some sort... The fact that the cories seem more heavily hit also leads me to think they picked up something from the substrate.

What I also know is that my water supply did change in the late fall... I learned my city has an auxiliary water supply from a different reservoir when water levels are high enough. That is when my KH must have changed and pH got altered slightly at one point and my nitrates went to 0 (it briefly freaked me out but once I realized that my ammonia and nitrites stayed a 0, and my GH remained stable, I was happy about it.) I also learned to monitor my tap water, as well as what is in my tank, for this very reason. I don't think any of this has to do with the deaths in my tanks at all. Other than the KH dropping a little bit, nothing else has changed. Pretty happy with my parameters.


In sum, the symptoms line up with a gill infection of some sort so I am willing to give Andy's idea a try.

 

[Andy Sager]

So here's what I do know--the primary symptoms are inflamed gills, heavy pumping of gills, darting/flashing, eventually bloating and death (in the end stages.) I know that heavy water changes and thorough gravel vacuuming certainly haven't hurt (possibly help a very small bit), but hasn't been a cure. I am doing two 20% water changes a week at this point. I know this tank is not overstocked and, other than a lower KH than I ideally want, the water parameters are spot on. The care I give them is good. I am pre filtering through carbon and pre-aerating my water. I also know that this started after the addition of new fish, which also leads me to believe it is an infection of some sort... The fact that the cories seem more heavily hit also leads me to think they picked up something from the substrate.

What I also know is that my water supply did change in the late fall... I learned my city has an auxiliary water supply from a different reservoir when water levels are high enough. That is when my KH must have changed and pH got altered slightly at one point and my nitrates went to 0 (it briefly freaked me out but once I realized that my ammonia and nitrites stayed a 0, and my GH remained stable, I was happy about it.) I also learned to monitor my tap water, as well as what is in my tank, for this very reason. I don't think any of this has to do with the deaths in my tanks at all. Other than the KH dropping a little bit, nothing else has changed. Pretty happy with my parameters.


In sum, the symptoms line up with a gill infection of some sort so I am willing to give Andy's idea a try.

Hopefully the meds work and it's not too late. Yours is just another example on the need to quarantine new fish these days. Today's fish carry so many things that your fish don't want.

 

[Colin_T]

Inflamed gills and breathing heavily can be caused by poor water quality, chemicals in the water, gill flukes, a bacterial or fungal infection on the gill filaments (this is uncommon). Gill flukes and poor water quality are the most common causes. Praziquantel or salt can treat gill flukes.

Darting/ flashing/ rubbing on objects can be from poor water quality, chemicals or external protozoan infections. External protozoan infections show up as cream, white or grey patches over part/s of the body. You can treat it with salt or Malachite Green, which is a carcinogen. Salt is a lot safer.

Sudden bloating (happens overnight) is internal organ failure and can be caused by bacterial infections in the organs or the organs fail due to chemicals, salt or minerals. Salt and minerals can damage the kidneys and other organs of soft water fishes if the fish are exposed to salt or lots of minerals for a period of time (more than a month). Salt and minerals generally don't harm fish from hard water. Death generally occurs in 24-48 hours of the bloating.

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Metronidazole won't do anything for the gill problems. If you want to use praziquantel, try to find some on its own so you aren't adding antibiotics to the aquariums.

Salt can treat a number of minor bacterial, fungal and protozoan infections, as well as gill flukes.

 

[larochem595]

Hopefully the meds work and it's not too late. Yours is just another example on the need to quarantine new fish these days. Today's fish carry so many things that your fish don't want.

I agree... This is a perfect case and point of the importance of quarantine.

 

[Andy Sager]

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Metronidazole won't do anything for the gill problems. If you want to use praziquantel, try to find some on its own so you aren't adding antibiotics to the aquariums.

Salt can treat a number of minor bacterial, fungal and protozoan infections, as well as gill flukes.

I hate to keep bumping heads but this is a description for Metronidazole: This medication works to soothe and treat infected eyes, fin or tail rot, skin ulcerations, pop-eye, columnaris disease, and gill disease.
And this is for Metroplex ( the brand name for Metronidazole ): is an effective and safe treatment for several protozoan and anaerobic bacterial diseases of fish.

Since the cause of the OP's gill issue is unknown, why would you not want to treat with it in combination with Praziquantel as an overall antibacterial-antiprotozoan-antiparasitic med?

 

[Colin_T]

I hate to keep bumping heads but this is a description for Metronidazole: This medication works to soothe and treat infected eyes, fin or tail rot, skin ulcerations, pop-eye, columnaris disease, and gill disease.
And this is for Metroplex ( the brand name for Metronidazole ): is an effective and safe treatment for several protozoan and anaerobic bacterial diseases of fish.

Since the cause of the OP's gill issue is unknown, why would you not want to treat with it in combination with Praziquantel as an overall antibacterial-antiprotozoan-antiparasitic med?

Adding antibiotics willy nilly to an aquarium when the disease is undiagnosed is one of the reasons we have drug resistant bacteria killing birds, fish, reptiles, people and animals all around the world. Antibiotics should only be used on known bacterial infections that have not responded to normal treatments. Normal treatments in fish can range from salt, to liquid medications with Formaldehyde, Acriflavine, Methylene Blue, etc.

Information on a company's website about this product doing this that and all the rest should be taken with a grain of salt. I have had discussions with SeaChem and a few other companies about false and misleading advertising on their sites. They refuse to change their webpages and in their responses basically said fish keepers were stupid. If a website shows pictures and provides a description of each disease, and lists all the possible causes and various treatments, then it's a different story. That would be a good website to use. But websites from chemical manufacturers and companies that want to sell you stuff should have the correct information readily available to anyone who visits their site. They should not just say our product treats this, this, this and this, when it doesn't treat all of those things.

In my experience, Metronidazole does nothing to treat Columnaris, ulcers, pop-eye, or fin and tail rot. Fin rot is normally caused by poor water quality and can be treated with salt and water changes.

Most eye infections are caused by scratching or damaging the outer surface of the eye and will normally heal without any treatment if the water is good and the tank is clean. A bit of salt can be used to help reduce the chance of secondary infections.

Ulcers can be caused by a number of different types of flesh eating bacteria and in rainbowfish ulcers are a sign of Mycobacterium infection, which can't be treated.

Columnaris does need antibiotics but it needs the correct antibiotic, and a lot of people misdiagnose other diseases for Columnaris. They treat the tank with antibiotics and it does nothing. Most of the time fish diagnosed with Columnaris actually have an external protozoan infection or are producing excess mucous caused by poor water quality.

Just because antibiotics are readily available in some countries when they shouldn't be due to drug resistance, it doesn't mean they should be the first choice when it comes to treatment for anything. The OP has already used Doxycycline and it did nothing so adding more antibiotics is unlikely to help the fish but is likely to increase the risk of the aquarium developing drug resistant bacteria.

 

[larochem595]

Adding antibiotics willy nilly to an aquarium when the disease is undiagnosed is one of the reasons we have drug resistant bacteria killing birds, fish, reptiles, people and animals all around the world. Antibiotics should only be used on known bacterial infections that have not responded to normal treatments. Normal treatments in fish can range from salt, to liquid medications with Formaldehyde, Acriflavine, Methylene Blue, etc.

Information on a company's website about this product doing this that and all the rest should be taken with a grain of salt. I have had discussions with SeaChem and a few other companies about false and misleading advertising on their sites. They refuse to change their webpages and in their responses basically said fish keepers were stupid. If a website shows pictures and provides a description of each disease, and lists all the possible causes and various treatments, then it's a different story. That would be a good website to use. But websites from chemical manufacturers and companies that want to sell you stuff should have the correct information readily available to anyone who visits their site. They should not just say our product treats this, this, this and this, when it doesn't treat all of those things.

In my experience, Metronidazole does nothing to treat Columnaris, ulcers, pop-eye, or fin and tail rot. Fin rot is normally caused by poor water quality and can be treated with salt and water changes.

Most eye infections are caused by scratching or damaging the outer surface of the eye and will normally heal without any treatment if the water is good and the tank is clean. A bit of salt can be used to help reduce the chance of secondary infections.

Ulcers can be caused by a number of different types of flesh eating bacteria and in rainbowfish ulcers are a sign of Mycobacterium infection, which can't be treated.

Columnaris does need antibiotics but it needs the correct antibiotic, and a lot of people misdiagnose other diseases for Columnaris. They treat the tank with antibiotics and it does nothing. Most of the time fish diagnosed with Columnaris actually have an external protozoan infection or are producing excess mucous caused by poor water quality.

Just because antibiotics are readily available in some countries when they shouldn't be due to drug resistance, it doesn't mean they should be the first choice when it comes to treatment for anything. The OP has already used Doxycycline and it did nothing so adding more antibiotics is unlikely to help the fish but is likely to increase the risk of the aquarium developing drug resistant bacteria.

i work in healthcare and am aware of the dangers of antibiotic resistance--I would not say I am treating things "willy nilly.". I take things cautiously and thoughtfully. This has been insidious and going on for over a month. I have ruled out water quality/cycling issues. I am treating an actual infection. Ideally, I wish I had a culture to figure out exactly what's going on but I don't think there's anyone locally who could do such a thing...it would be cool if they did because I could really pinpoint treatment.

With antibiotics, I follow dosing guidelines and the proper water changes to a T. I fully complete the course, like one should do with antibiotics. My fish will always be isolated in this aquarium (especially given that there's likely a pathogen infecting the fish, I'd never give them away) so the spreading of antibiotic resistant bacteria to the outside world isn't a concern. I think that this sort of thing becomes an issue for wholesalers or stores who would be treating large volumes of fish and sending them out and then fish might get repeatedly treated. I'm also not concerned about my tank itself developing antibiotic resistance as I do not overuse these kind of things...

I wish I had a way to culture whatever might be my issue. Otherwise I am left treating symptoms, regardless of whatever meds I choose.

 

[Colin_T]

If you contact your local Department of Agriculture, they might have a Fish Health department who might be able to culture samples. However, they usually kill the fish you take in to be tested. They don't normally charge home aquarists, but do charge businesses. But if they have a Fish Health department nearby and do necropsies, ask them what the price is for home fish keepers.

If this fish dies, then see about taking it in to be tested to try and find out what is causing the problem. Then if it happens again, further down the track, you might have more information to go on.

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Whilst you work in the health profession and take every precaution to avoid drug resistance, you don't know what the fish were treated with before you got them. In Asian fish farms, fish are regularly treated with "medications" that shouldn't be used, and this includes antibiotics. The fish can have drug resistant bacteria before they even come into your country. Then the importer/ wholesaler might treat them for something, and the shop might treat them for something too. By the time you get the fish, they could have been treated with a dozen different chemicals and various antibiotics.

I have actually seen shipments of fish die from lack of chemicals. The fish had been treated so many times they were literally addicted to chemicals, they were drug addicted fish. It took us a while to work out what was going on and when we did, we had to put medications back into the water to keep them alive and then wean them off it over a month. We ended up changing supplier because it wasn't good. These fish were coming from a supplier in Indonesia who regularly put antibiotics and other types of chemicals in the water they shipped the fish in. Apparently this was common practice where these fish were coming from. I'm not saying all suppliers do this and I doubt it would happen in most countries, but you don't know the history of the fish and that could be a factor in this issue.

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Ideally, if you need/ want to use antibiotics, try to use them in a bare container with a few plastic plants, an airstone and a heater. This means there are fewer microscopic organisms in the container and water and the medication can work on the fish instead of on everything else in the tank.

 

[larochem595]

If you contact your local Department of Agriculture, they might have a Fish Health department who might be able to culture samples. However, they usually kill the fish you take in to be tested. They don't normally charge home aquarists, but do charge businesses. But if they have a Fish Health department nearby and do necropsies, ask them what the price is for home fish keepers.

If this fish dies, then see about taking it in to be tested to try and find out what is causing the problem. Then if it happens again, further down the track, you might have more information to go on.

-------------------

Whilst you work in the health profession and take every precaution to avoid drug resistance, you don't know what the fish were treated with before you got them. In Asian fish farms, fish are regularly treated with "medications" that shouldn't be used, and this includes antibiotics. The fish can have drug resistant bacteria before they even come into your country. Then the importer/ wholesaler might treat them for something, and the shop might treat them for something too. By the time you get the fish, they could have been treated with a dozen different chemicals and various antibiotics.

I have actually seen shipments of fish die from lack of chemicals. The fish had been treated so many times they were literally addicted to chemicals, they were drug addicted fish. It took us a while to work out what was going on and when we did, we had to put medications back into the water to keep them alive and then wean them off it over a month. We ended up changing supplier because it wasn't good. These fish were coming from a supplier in Indonesia who regularly put antibiotics and other types of chemicals in the water they shipped the fish in. Apparently this was common practice where these fish were coming from. I'm not saying all suppliers do this and I doubt it would happen in most countries, but you don't know the history of the fish and that could be a factor in this issue.

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Ideally, if you need/ want to use antibiotics, try to use them in a bare container with a few plastic plants, an airstone and a heater. This means there are fewer microscopic organisms in the container and water and the medication can work on the fish instead of on everything else in the tank.

It often makes me sad to think how fish are treated in this hobby, both by stores and suppliers. I think sometimes chemicals are added before shipping internationally to prevent spread of diseases...in some instances it might be required by customs and the USDA. But, I think that some less legit overseas breeders probably just throw whatever at them and don't properly treat.

I have yet to find a store in my neck of the woods I particularly care for. There was one store (now closed, thank goodness) that would markdown fish that were unwell to try to unload them (often to people who were uneducated about the warning signs like clamped fins or frayed fins, etc.) I recall seeing a tank of discus that had a few fish with such horrible infections and badly frayed tail fins that they barely had a stub to swim. To leave them like that without proper treatment seemed so inhumane. That practice irritated me so bad I never went back there.

Anyways, I digress...

If this round of meds doesn't help, I will see about getting a culture. I discovered that there is a local zoo that actually does cultures for pet owners and hobbyists but it's like over an hour away so it might be tricky to get up there... Sick day for my aquarium???

 

[Andy Sager]

Adding antibiotics willy nilly to an aquarium when the disease is undiagnosed is one of the reasons we have drug resistant bacteria killing birds, fish, reptiles, people and animals all around the world. Antibiotics should only be used on known bacterial infections that have not responded to normal treatments. Normal treatments in fish can range from salt, to liquid medications with Formaldehyde, Acriflavine, Methylene Blue, etc.

Information on a company's website about this product doing this that and all the rest should be taken with a grain of salt. I have had discussions with SeaChem and a few other companies about false and misleading advertising on their sites. They refuse to change their webpages and in their responses basically said fish keepers were stupid. If a website shows pictures and provides a description of each disease, and lists all the possible causes and various treatments, then it's a different story. That would be a good website to use. But websites from chemical manufacturers and companies that want to sell you stuff should have the correct information readily available to anyone who visits their site. They should not just say our product treats this, this, this and this, when it doesn't treat all of those things.

In my experience, Metronidazole does nothing to treat Columnaris, ulcers, pop-eye, or fin and tail rot. Fin rot is normally caused by poor water quality and can be treated with salt and water changes.

Most eye infections are caused by scratching or damaging the outer surface of the eye and will normally heal without any treatment if the water is good and the tank is clean. A bit of salt can be used to help reduce the chance of secondary infections.

Ulcers can be caused by a number of different types of flesh eating bacteria and in rainbowfish ulcers are a sign of Mycobacterium infection, which can't be treated.

Columnaris does need antibiotics but it needs the correct antibiotic, and a lot of people misdiagnose other diseases for Columnaris. They treat the tank with antibiotics and it does nothing. Most of the time fish diagnosed with Columnaris actually have an external protozoan infection or are producing excess mucous caused by poor water quality.

Just because antibiotics are readily available in some countries when they shouldn't be due to drug resistance, it doesn't mean they should be the first choice when it comes to treatment for anything. The OP has already used Doxycycline and it did nothing so adding more antibiotics is unlikely to help the fish but is likely to increase the risk of the aquarium developing drug resistant bacteria.

I guess this is where our experiences working with medicines differ. I don't recommend medicines willy nilly and I do meds specific to water conditions as well as symptoms.
I do know that sometimes you have to " shoot the moon" and try meds to see if they work. Especially when you don't have a confirmed diagnosis. I've experienced this with both humans and animals. Using a med one time to treat one episode does not create a resistance. It's a continual use when not necessary that does.
I have done cultures on fish before and have sometimes been surprised at the results. Drugs not supposed to work under a condition that cultured to be the most effective. It's crazy. Just because one antibiotic didn't work does not mean that all antibiotics won't work. I also know that salt is the the cure all for every situation. You can kill fish with salt just as much as you can with a medication.
Here in the states, not every government agency will work with a person off the street. They may supply you with information but that's where it ends. Most fish related things need to be done through universities that deal with marine sciences. Florida fish farmers in Tampa area use the University of Florida clear on the opposite side of the state. When they were in S. Florida they used the University of Miami as both of these have top notch marine science education. That can't be said for everywhere in the U.S.

But the bottom line is that PROPER diagnosis is the most important thing to accurately treat a condition however, and I have experienced this in one of my hatcheries, not every condition has had a previous diagnosis so no information could be given as all information was new. As we move further away from books and closer to the internet, it gets harder and harder to get good medical advice for fish whereas there are some excellent books on fish diseases. Sadly, most people would prefer free bad information than good expensive information.

 

[larochem595]

Ugh...
Lost my smallest oto on Friday night. Same thing that has been plaguing my tank--heavy pumping of gills, lethargic, bloated (this one was swimming in circles due to bloating.) I wanted to have it cultured but there was no way I could get it somewhere over an hour away because of other responsibilities. Plus, it's just a teensy oto...not sure how easy it would be to use that for a culture.

I ended up euthanizing the oto because I knew it wouldn't last overnight. So sad... I hate working so hard to keep losing fish but I think I made the right call, rather than letting a sick fish linger. During this chunk of time, my lone Cory was also struggling with heavy gill pumping but it appears to be pulling through at the moment. I am really sad because I genuinely want my tank to do well ? One additional observation--theres a cyclical nature to this--the fish will appear to be ok for a chunk of time, then start gradually doing poorly, then I'll do a water change and a day later they seem slightly better.

Unfortunately, there's no decent shops in my neck of the woods, so needed to order meds online. I am still waiting for that to come in. I ordered both PraziPro as well as a Prazi Metro mix.

My plan for my tank is this: (comments/ideas are welcome)
--Medicate when the meds come in
--If things don't improve, let things take their natural course, then break down my tank, disinfect and start over.... cycling and all. This tank would be restarted as a livebearer tank, as the tank and my water parameters would be more suited for that.
--If things get better, I'd leave things alone until it's good and stable.

Thanks for reading!

 

[Andy Sager]

Ugh...
Lost my smallest oto on Friday night. Same thing that has been plaguing my tank--heavy pumping of gills, lethargic, bloated (this one was swimming in circles due to bloating.) I wanted to have it cultured but there was no way I could get it somewhere over an hour away because of other responsibilities. Plus, it's just a teensy oto...not sure how easy it would be to use that for a culture.

I ended up euthanizing the oto because I knew it wouldn't last overnight. So sad... I hate working so hard to keep losing fish but I think I made the right call, rather than letting a sick fish linger. During this chunk of time, my lone Cory was also struggling with heavy gill pumping but it appears to be pulling through at the moment. I am really sad because I genuinely want my tank to do well �� One additional observation--theres a cyclical nature to this--the fish will appear to be ok for a chunk of time, then start gradually doing poorly, then I'll do a water change and a day later they seem slightly better.

Unfortunately, there's no decent shops in my neck of the woods, so needed to order meds online. I am still waiting for that to come in. I ordered both PraziPro as well as a Prazi Metro mix.

My plan for my tank is this: (comments/ideas are welcome)
--Medicate when the meds come in
--If things don't improve, let things take their natural course, then break down my tank, disinfect and start over.... cycling and all. This tank would be restarted as a livebearer tank, as the tank and my water parameters would be more suited for that.
--If things get better, I'd leave things alone until it's good and stable.

Thanks for reading!

The scenario you describe sounds as much like a water quality issue as a disease issue. Are you doing full panel testing?( Ph, GH,KH, Ammonia, Nitrite, nitrate) The fact that the fish act better after a water change is what makes me lean this way. The problem is that many fish parasites have an on fish stage and off fish stage so it's not unusual for there to be cycles of they look good, no they don't, yes they do, no they don't.
For water quality issues: Is there anything metallic in the tank within your decorations? What about calcium based rocks/ shells? Do you see any rust stains on anything tank related? The issue could also caused by any additives you are using. You mentioned previously that you were adding alkalinity buffers. Most Otos are wild caught so they come from soft acidic waters that are closer to neutral in Ph. Alkalinity buffers are not necessary for these fish. They also come from slow flowing water areas. Does this match your water conditions?

 

[larochem595]

The scenario you describe sounds as much like a water quality issue as a disease issue. Are you doing full panel testing?( Ph, GH,KH, Ammonia, Nitrite, nitrate) The fact that the fish act better after a water change is what makes me lean this way. The problem is that many fish parasites have an on fish stage and off fish stage so it's not unusual for there to be cycles of they look good, no they don't, yes they do, no they don't.
For water quality issues: Is there anything metallic in the tank within your decorations? What about calcium based rocks/ shells? Do you see any rust stains on anything tank related? The issue could also caused by any additives you are using. You mentioned previously that you were adding alkalinity buffers. Most Otos are wild caught so they come from soft acidic waters that are closer to neutral in Ph. Alkalinity buffers are not necessary for these fish. They also come from slow flowing water areas. Does this match your water conditions?

When I tested on Friday (before water change)
Ph-7.5 (baseline)
Ammonia -0
Nitrates-10
KH-2
GH-7

I use buffers to bring up my KH, which is otherwise undetectable. It would be a 0 otherwise.
The whole "look good, don't look good, look okay, no they don't..." seems like what I am experiencing. I am definitely banging my head against a wall. There are definite good days and bad. I am trying to figure out a pattern... I would say that it's roughly 1 day after a water change that they look best but it doesn't seem like a hard rule. They had a 20% change on Friday night. Today I don't see any major signs of struggling but they still seem slightly reddened around the gills, even though their behavior looks normal.

Nothing calcium based like shells. Nothing rusty I can think of.

I added pictures to see if you guys see anything... One of the otos was too interested in the glass and plants in the back so couldn't snap a picture of that one. The pictures are all of the same oto.

 

[Andy Sager]

If that is wood I see in the pictures, you are probably knocking your head against the wall with adding buffers because the wood is softening your water. Carbonate hardness (KH) value is really just the ability to buffer water to prevent Ph swings. Ph swings are worse for fish than a steady one is but over the course of a day, the Ph can swing naturally. The wood would be removing whatever Kh is in your water and lowering your Ph. So you are basically feeding your wood when you add the buffers.

I do not see anything wrong with the fish in the pictures so I make this suggestion, if the water you use to refill your tank during a water change has a Kh level between 4-8 dKH, remove the wood from the aquarium and do not add any buffers and see how long the fish continue to look good. If there is still a low KH value and the fish look good, the problem was your wood's interaction with the hardness levels. If there is high Kh level in your refill water and the fish look stressed again, I would suggest preparing your refill water in a separate container to have a KH level of 4-8 dKH before adding it back to the tank. (I would surmise that since the fish looked better the day after the water change even tho there was a high KH level in the refill water, the wood would absorb enough of it to lower the level to their comfort level. This really should apply more for the GH but hopefully without using the buffers, the Gh will be lower as well. If not, you will need to adjust that as well before adding the water back into the tank. ) Overall, Otos ( and some Cory species) come from very soft, acidic waters so "hardness" is the enemy. You need some to prevent the Ph swings but not so much that it effects the fish.

 

[larochem595]

If that is wood I see in the pictures, you are probably knocking your head against the wall with adding buffers because the wood is softening your water. Carbonate hardness (KH) value is really just the ability to buffer water to prevent Ph swings. Ph swings are worse for fish than a steady one is but over the course of a day, the Ph can swing naturally. The wood would be removing whatever Kh is in your water and lowering your Ph. So you are basically feeding your wood when you add the buffers.

I do not see anything wrong with the fish in the pictures so I make this suggestion, if the water you use to refill your tank during a water change has a Kh level between 4-8 dKH, remove the wood from the aquarium and do not add any buffers and see how long the fish continue to look good. If there is still a low KH value and the fish look good, the problem was your wood's interaction with the hardness levels. If there is high Kh level in your refill water and the fish look stressed again, I would suggest preparing your refill water in a separate container to have a KH level of 4-8 dKH before adding it back to the tank. (I would surmise that since the fish looked better the day after the water change even tho there was a high KH level in the refill water, the wood would absorb enough of it to lower the level to their comfort level. This really should apply more for the GH but hopefully without using the buffers, the Gh will be lower as well. If not, you will need to adjust that as well before adding the water back into the tank. ) Overall, Otos ( and some Cory species) come from very soft, acidic waters so "hardness" is the enemy. You need some to prevent the Ph swings but not so much that it effects the fish.

So I treat my water in a bucket prior to adding it to the tank. The problem is that out of the tap, the KH of my city water is 0. With buffers, the KH of my tank and the water in my bucket prior to change is a 2.

 

[Andy Sager]

So I treat my water in a bucket prior to adding it to the tank. The problem is that out of the tap, the KH of my city water is 0. With buffers, the KH of my tank and the water in my bucket prior to change is a 2.

There has to be a correlation between the water change and the fish looking good and time which makes the fish look bad. That would mean that something in the tank is making the fish not happy. I would still start with removing any wood from the tank as that will remove your buffer from the water.
Inflamed gills can be from ammonia poisoning, gill flukes, proliferative gill disease, bacterial gill disease to name a few. I would eliminate ammonia poisoning since the water change helps but time doesn't and your test said 0 before the water change. I would eliminate flukes as well since the fish recover after the water change but reappear poorly over time. PGD and Bacterial gill disease should get worse over time and not respond to just a water change so that pretty much eliminates them. So we are back to something in the water.
Your GH is not all that high but have you tested your tap water's GH? If it's higher than 7 but over time goes down from being absorbed by the wood, that would show that the fish are lacking the minerals found in water since they get better after the water change. If it's lower than 7 but is rising, that means there is a mineral based product in the tank that is leeching out causing the GH to rise and the rise is too much for the fish. That would mean you need to take a really good look at what decor you have in the tank. If it's 7, I'd take a sample of your water to a local LFS to have them confirm your readings.
If confirmed, post a full tank picture so we can see what else is in the tank.