Help Needed with Fish Mortality Issue in My Aquarium

[Mraqualover]

Good evening, everyone. I know this forum is mainly for cichlids, but I need your help with a problem that has come up. I appreciate any assistance you can provide.

Information:I have two aquariums, both 60 liters: one cube-shaped and one rectangular. The rectangular tank has a JBL e702 filter, which is more than sufficient for the aquarium. In fact, I had to direct the filter output towards the glass because my latest addition (a Blue German Ram) didn't like the strong water movement. This tank is planted and houses four Leopard Danios, two Cherry Barbs, one Blue German Ram, and some shrimp.

The cube tank has a SLIM FILTER JINX 638-H hang-on-back filter. It contains various plants, including floating plants, and previously had eight Galaxy Rasboras (six added recently and two older ones), along with many shrimp.

Problem:Last night, all eight Galaxy Rasboras were present. However, this afternoon I found four of them dead, including the two older ones that had been well-acclimated for over three months.

Possible Causes:

1. Water Parameters: I tested the water and found 0 nitrites and 0 ammonia. However, when setting up this tank, I left some openings in the driftwood and between some stones that create pockets where water flow might be restricted. I'm unsure if these areas could have different parameters, but I doubt it would result in both ammonia and nitrites being at zero.
2. Nitrate Levels: The nitrate levels in both tanks have been high, above 50 ppm. Normally, I use well water that has about 20 ppm of nitrates. This time, I decided to use treated tap water with a nitrate concentration below 10 ppm. I left the tap water in open containers on my balcony for two days to dissipate the chlorine. Yesterday was the first time I added tap water to the tanks. In the cube tank, I replaced about 10% of the water. I doubt this caused the issue since I replaced 50% in the rectangular tank with no fatalities.
3. New Fish Quarantine: I did not quarantine the six new Galaxy Rasboras before adding them to the tank, so they might have brought a disease. However, it's strange that my two older fish died first before the newer ones and that four fish died within a day.

Observation:This morning, before leaving home, I noticed the fish were swimming near the surface, which is unusual.

Question:Does anyone have any idea what might be causing this issue and what I should do now that the damage is done?

 

[MacZ]

Care to fill out the things that are not covered by your post?

Template for disease/parasite/death cases

This template contains the most important questions to be answered when dealing with sick or dead fish to find causes and advise on treatments. Please copy and paste into a new thread and answer the questions as precise as possible. Water parameters should be given in numbers. "Fine" or "good"...

apistogramma.com

Especially of importance are things like chronology of the events, like when did you get the new additions and how long have you had them and the like. There are several other questions in the template, that will be helpful if answered. And please add a picture of the tank and fish.

But one thing I can tell you already:

Possible Causes:

1. Water Parameters: I tested the water and found 0 nitrites and 0 ammonia. However, when setting up this tank, I left some openings in the driftwood and between some stones that create pockets where water flow might be restricted. I'm unsure if these areas could have different parameters, but I doubt it would result in both ammonia and nitrites being at zero.
2. Nitrate Levels: The nitrate levels in both tanks have been high, above 50 ppm. Normally, I use well water that has about 20 ppm of nitrates. This time, I decided to use treated tap water with a nitrate concentration below 10 ppm. I left the tap water in open containers on my balcony for two days to dissipate the chlorine. Yesterday was the first time I added tap water to the tanks. In the cube tank, I replaced about 10% of the water. I doubt this caused the issue since I replaced 50% in the rectangular tank with no fatalities.

Those are for sure NOT connected to your losses. The first is just overthinking, the second is... nitrate has only longterm effects in high levels, concentration swings of nitrate have no immediate effect whatsoever and indeed the water you left out can't be the cause either, as then you would have at least 75% fatalities in both tanks. And by the way... in which country do you live? Maybe there is even no need for any chlorine precautions. I'm asking because JBL is mostly in use in countries that don't chlorinate in their whole supply system.

New Fish Quarantine: I did not quarantine the six new Galaxy Rasboras before adding them to the tank, so they might have brought a disease. However, it's strange that my two older fish died first before the newer ones and that four fish died within a day.

Now that's a plausible thought. One of the most common things to happen, actually. I just can't tell for sure without more info.

And a well meant advise to get useful answers: Always try to just tell people what happened and the facts about your tank, then let them come to a conclusion themselves. Telling your suspicions can make people blind to other things.

 

[Mraqualover]

Care to fill out the things that are not covered by your post?

Template for disease/parasite/death cases

This template contains the most important questions to be answered when dealing with sick or dead fish to find causes and advise on treatments. Please copy and paste into a new thread and answer the questions as precise as possible. Water parameters should be given in numbers. "Fine" or "good"...

apistogramma.com

Especially of importance are things like chronology of the events, like when did you get the new additions and how long have you had them and the like. There are several other questions in the template, that will be helpful if answered. And please add a picture of the tank and fish.

But one thing I can tell you already:

Those are for sure NOT connected to your losses. The first is just overthinking, the second is... nitrate has only longterm effects in high levels, concentration swings of nitrate have no immediate effect whatsoever and indeed the water you left out can't be the cause either, as then you would have at least 75% fatalities in both tanks. And by the way... in which country do you live? Maybe there is even no need for any chlorine precautions. I'm asking because JBL is mostly in use in countries that don't chlorinate in their whole supply system.


Now that's a plausible thought. One of the most common things to happen, actually. I just can't tell for sure without more info.

And a well meant advise to get useful answers: Always try to just tell people what happened and the facts about your tank, then let them come to a conclusion themselves. Telling your suspicions can make people blind to other things.

You’re right; I didn't see the template earlier. Apologies for that. Here are the necessary details:

Cube Aquarium Dimensions: 40x40x40 cm

Setup Duration: 3-4 months

Initial Fish Addition:

• I initially added 3 Galaxy Rasboras to this tank, but they never ate and eventually died. I thought this was due to the age because they look very young and small.
• About two weeks later, I transferred 3 Galaxy Rasboras from my other tank, which had been there for about 2 years. One of these seemed thin with a strange shape, but he always looked like that, so I didn't think it was a disease. However, he died a few weeks after being in the new tank.
• These last two Rasboras (one male and one female) lived in the cube tank for about two months.

Recent Fish Addition:

• Last Saturday, I visited a new store and bought 6 more Galaxy Rasboras because I noticed my existing two seemed lonely and this ones seemed older and bigger than the last ones. I didn't quarantine the new fish and added them directly to the tank.
• Over the past few days, the new Rasboras didn’t seem to be eating, so I increased the amount of food.

Water Testing and Changes:

• I decided to test the water because I added a Blue German Ram to my rectangular tank and wanted to ensure the conditions were good.
• I discovered that the nitrate levels in my rectangular tank were over 100 ppm, likely due to overfeeding.
• This prompted me to test the water in the cube tank, which had nitrate levels around 50 ppm. This led me to perform water changes.
• Despite the new Rasboras not appearing to eat, they seemed active in the tank. However, about two days ago, they started hiding more, which I attributed to fear.
• This morning, I noticed some fish were near the surface but didn’t think much of it. When I returned home, I found three dead and one missing.

Water Parameters:

• NO3: 0
• NO2: 0
• pH: around 7.5
• KH: 4
• GH: 6
• I use ZOOLEK liquid test kits.

Maintenance and Feeding:

• I usually perform a 25% water change every 3 weeks.
• Recently used a liquid micro fertilizer from Aquili.
• I also have a CO2 spray, which I use every two days.
• Fish are fed frozen food; recently, I switched to DISCUS Quintet from Ocean Nutrition as my usual Tropical Quintet was unavailable. I was told it would be a suitable alternative.
• I feed the fish with frozen food every other day, and on alternate days, I use Community Formula pellets from the same brand.

In this image, the fish exhibits strange behavior compared to the others. I don't know if this makes sense, but while the others swim with their fins opening and closing, this one always keeps its fins closed, almost as if it's curled up.

 

[Mraqualover]

Care to fill out the things that are not covered by your post?

Template for disease/parasite/death cases

This template contains the most important questions to be answered when dealing with sick or dead fish to find causes and advise on treatments. Please copy and paste into a new thread and answer the questions as precise as possible. Water parameters should be given in numbers. "Fine" or "good"...

apistogramma.com

Especially of importance are things like chronology of the events, like when did you get the new additions and how long have you had them and the like. There are several other questions in the template, that will be helpful if answered. And please add a picture of the tank and fish.

But one thing I can tell you already:

Those are for sure NOT connected to your losses. The first is just overthinking, the second is... nitrate has only longterm effects in high levels, concentration swings of nitrate have no immediate effect whatsoever and indeed the water you left out can't be the cause either, as then you would have at least 75% fatalities in both tanks. And by the way... in which country do you live? Maybe there is even no need for any chlorine precautions. I'm asking because JBL is mostly in use in countries that don't chlorinate in their whole supply system.


Now that's a plausible thought. One of the most common things to happen, actually. I just can't tell for sure without more info.

And a well meant advise to get useful answers: Always try to just tell people what happened and the facts about your tank, then let them come to a conclusion themselves. Telling your suspicions can make people blind to other things.

And i am from Portugal

 

[MacZ]

Allright, first things first: Thank you for filling out the template, very helpful.

Well I see more than one problem but only one directly concerns the fish.
It seems indeed that you started out with not-so-good stock in the first place, good quality D. margaritatus are not easy to come by, most of the available stock in Europe is sickly from the start. In combination with new fish added without quarantine, I'd presume the new arrivals were just as helpless against the pathogens already present as were the old ones to the pathogens introduced by the new ones. Happens a lot. The timeframe tells me either a bacterial problem or a skin/gill parasite.
If it's the former you can't do anything about it, as here in the EU antibiotics do not go over the counter without a prescription. And in this case I doubt a vet will just give you some, so best you can do is waiting it out and optimize the tank conditions. (more on that below)
If it's the latter you would be observing the fish being near the surface a lot more often, and heavily pumping with their gills all the time. As you don't mention this I would rule that out.
So It boils down to the new fish, new pathogen problem in both directions. Nothing unusual, sadly. And something you can't do anything about in hindsight. Quarantining is key to prevent this. In a quarantine tank the new arrivals can be acclimated to the pathogens in your tanks by adding small portions of tankwater into the quarantine tank during the observation period and once it's clear the new fish haven't brought any parasites and the like, water from the quarantine should be added to the tank they're about to go a week before moving them, so the old fish can acclimate to whatever microbiome they have brought with them.

Additionally: Throw away the discus food. It's already a big problem feeding beef heart and similar stuff to Discus, it's a fattening food to raise Discus fry to sale size quickly. It comes with the necessity of raising temperatures very high, so the stuff can even be digested. No fish really needs something like it, from a nutritional point of view.
You can of course feed frozen, but stick to things like Artemia, Daphnia, Cyclops, Copepods and white mosquito larvae, maybe also offer those live whenever possible. Also: Always thaw frozen food so the water portion of it doesn't spoil the tankwater.
- - - - -

The second problem I see is your maintenance and doesn't have much impact on fish health. For a tank running less than a year 25% waterchange in 3 weeks is far from ideal. For the first 6 months 50% a week is advisable, after 12 months the tank should have seasoned so far one can look if it is necessary still. Many standard tanks can go with 25-50% every two weeks once they have properly seasoned.

The high NO3 was not necessarily only from overfeeding but a combination of several things: First you have soil in your tank but barely any plants actually planted in it. Your main plant mass (the Anubias and Bucephalandra) doesn't draw nutrients from it, otherwise you have a lot of open substrate which is just sitting there leaching Nitrogen into the water. Additionally you add fertilizer, which I presume is a full spectrum including a nitrogen compund like ammonium which is metabolized by microorganisms in the tank into NO3 as well. The frozen food just added on top of this.
Now the kicker is: Anubias and Bucephalandra are very slow growing plants that don't use much nutrients. They also don't need a lot of lights and are very ok with no CO2 injection at all.

You have a big surplus of nutrients building up, which means waterchanges are even more necessary and should be more more frequent. Plus you unnecessarily add CO2 (which btw could be a reason for the fish being at the surface, do you have a CO2-Checker hidden somewhere in that tank?) Think of it like this: Nutrients, light and CO2 have to be balanced out for optimal plant growth. What you need exactly always depends on the plants. But if you raise one factor the others have to follow or nothing will happen. And if slow growing, undemanding plants meet strong light, high nutrients and CO2 injection not much will happen either. Nutrients rise until removed by waterchanges, CO2 stays unused, only pushing pH down temporarily and the lights cost you money in energy, but that's it. Or put in a metaphor: You're putting 21st century high octane jet fuel into a WWI double decker plane. Not gonna work out well.

A good way to help yourself with that is adding fast growing plants like Ceratophyllum (hornwort), Hydrocotyle (pennywort) or Elodea/Egeria (waterweeds) and floating plants like Salvinia (floating fern). All of these can be left floating, which makes them especially effective. Those suck up the surplus nutrients, while you can think about a new planting concept. You would do very well with stem plants and long root floaters like Limnobium (frogbit) in my opinion. You can most likely forego on the CO2 though.

So in conclusion:
- The fish can't really be helped much directly. The damage has been done, now you can only hope with good maintenance and care they stabilize. If not do proper quarantine next time you get fish and make sure to get healthy stock in the first place, so if you have doubts at the store, don't buy, but have a look elsewhere.
- The whole system needs a different maintenance and new plant concept. Once the tanks have seasoned with age and once you have the plants really going the fish should be doing better as well. Darrell ( @dw1305 ) and Ben ( @Ben Rhau ) know more about plants than me, hope they can help you out.

Just as a sidenote: You are aware M. ramirezi should be kept in really soft water (GH/KH below detection) and require fine sand as substrate? Hope the other tank offers at least the sand.

 

[Mraqualover]

Allright, first things first: Thank you for filling out the template, very helpful.

Well I see more than one problem but only one directly concerns the fish.
It seems indeed that you started out with not-so-good stock in the first place, good quality D. margaritatus are not easy to come by, most of the available stock in Europe is sickly from the start. In combination with new fish added without quarantine, I'd presume the new arrivals were just as helpless against the pathogens already present as were the old ones to the pathogens introduced by the new ones. Happens a lot. The timeframe tells me either a bacterial problem or a skin/gill parasite.
If it's the former you can't do anything about it, as here in the EU antibiotics do not go over the counter without a prescription. And in this case I doubt a vet will just give you some, so best you can do is waiting it out and optimize the tank conditions. (more on that below)
If it's the latter you would be observing the fish being near the surface a lot more often, and heavily pumping with their gills all the time. As you don't mention this I would rule that out.
So It boils down to the new fish, new pathogen problem in both directions. Nothing unusual, sadly. And something you can't do anything about in hindsight. Quarantining is key to prevent this. In a quarantine tank the new arrivals can be acclimated to the pathogens in your tanks by adding small portions of tankwater into the quarantine tank during the observation period and once it's clear the new fish haven't brought any parasites and the like, water from the quarantine should be added to the tank they're about to go a week before moving them, so the old fish can acclimate to whatever microbiome they have brought with them.

Additionally: Throw away the discus food. It's already a big problem feeding beef heart and similar stuff to Discus, it's a fattening food to raise Discus fry to sale size quickly. It comes with the necessity of raising temperatures very high, so the stuff can even be digested. No fish really needs something like it, from a nutritional point of view.
You can of course feed frozen, but stick to things like Artemia, Daphnia, Cyclops, Copepods and white mosquito larvae, maybe also offer those live whenever possible. Also: Always thaw frozen food so the water portion of it doesn't spoil the tankwater.
- - - - -

The second problem I see is your maintenance and doesn't have much impact on fish health. For a tank running less than a year 25% waterchange in 3 weeks is far from ideal. For the first 6 months 50% a week is advisable, after 12 months the tank should have seasoned so far one can look if it is necessary still. Many standard tanks can go with 25-50% every two weeks once they have properly seasoned.

The high NO3 was not necessarily only from overfeeding but a combination of several things: First you have soil in your tank but barely any plants actually planted in it. Your main plant mass (the Anubias and Bucephalandra) doesn't draw nutrients from it, otherwise you have a lot of open substrate which is just sitting there leaching Nitrogen into the water. Additionally you add fertilizer, which I presume is a full spectrum including a nitrogen compund like ammonium which is metabolized by microorganisms in the tank into NO3 as well. The frozen food just added on top of this.
Now the kicker is: Anubias and Bucephalandra are very slow growing plants that don't use much nutrients. They also don't need a lot of lights and are very ok with no CO2 injection at all.

You have a big surplus of nutrients building up, which means waterchanges are even more necessary and should be more more frequent. Plus you unnecessarily add CO2 (which btw could be a reason for the fish being at the surface, do you have a CO2-Checker hidden somewhere in that tank?) Think of it like this: Nutrients, light and CO2 have to be balanced out for optimal plant growth. What you need exactly always depends on the plants. But if you raise one factor the others have to follow or nothing will happen. And if slow growing, undemanding plants meet strong light, high nutrients and CO2 injection not much will happen either. Nutrients rise until removed by waterchanges, CO2 stays unused, only pushing pH down temporarily and the lights cost you money in energy, but that's it. Or put in a metaphor: You're putting 21st century high octane jet fuel into a WWI double decker plane. Not gonna work out well.

A good way to help yourself with that is adding fast growing plants like Ceratophyllum (hornwort), Hydrocotyle (pennywort) or Elodea/Egeria (waterweeds) and floating plants like Salvinia (floating fern). All of these can be left floating, which makes them especially effective. Those suck up the surplus nutrients, while you can think about a new planting concept. You would do very well with stem plants and long root floaters like Limnobium (frogbit) in my opinion. You can most likely forego on the CO2 though.

So in conclusion:
- The fish can't really be helped much directly. The damage has been done, now you can only hope with good maintenance and care they stabilize. If not do proper quarantine next time you get fish and make sure to get healthy stock in the first place, so if you have doubts at the store, don't buy, but have a look elsewhere.
- The whole system needs a different maintenance and new plant concept. Once the tanks have seasoned with age and once you have the plants really going the fish should be doing better as well. Darrell ( @dw1305 ) and Ben ( @Ben Rhau ) know more about plants than me, hope they can help you out.

Just as a sidenote: You are aware M. ramirezi should be kept in really soft water (GH/KH below detection) and require fine sand as substrate? Hope the other tank offers at least the sand.

Thank you very much for the help. Everything you said makes a lot of sense. Next time, I will quarantine the fish and use your method. I will also try to plant more in the soil to absorb the nutrients. My initial idea was to use slow-growing plants because they require less maintenance since they take longer to grow, and I really like this type of plant.

Regarding the rectangular tank, it does have fine sand for the ramirezi. I didn't put the ramirezi in the cube because the cube doesn't have sand, and I read that they really like sand. As for the GH and KH, I read that they can thrive in a GH range of 6-8 and a KH range of 1-4. In the case of KH, because it's a titration and the turning point is difficult to detect, the value is probably closer to 2, but I said 4 because it's the one I can distinguish more clearly.

I just wanted to share that I am buying a new aquarium with dimensions of 90x45x45 because I want more space for different kinds of fish and to accommodate a couple of ramirezi, as they need more space. The one I have now is a rectangular tank with dimensions of 60x30x30. So this new aquarium will be three times bigger. I will use the same filter (JBL e7002 with 700l/h). When I bought this filter, I asked for one that I could use in a larger aquarium in the future, but this came back to bite me because I didn't consider the strong current this filter creates in a small aquarium like mine, which really stresses the fish. Now I just need to buy a new light and a stronger heater to warm the water (this is important because houses in Portugal get really cold in the winter, and it is difficult to maintain the water temperature).

I am considering whether I should buy a professional CO2 system. I already have a drop checker, but I have never used it. If you have any ideas or advice that you or anyone else would like to share, I would be very grateful. Avoiding mistakes and keeping the fish happy is my top priority.

 

[MacZ]

I am considering whether I should buy a professional CO2 system. I already have a drop checker, but I have never used it. If you have any ideas or advice that you or anyone else would like to share, I would be very grateful. Avoiding mistakes and keeping the fish happy is my top priority.

Just a quick one, because I have to leave for work now: Just quit on the CO2, rather focus on plants that do well without injection. Especially if the fish are your priority, things like that are not useful at all.

 

[dw1305]

Hi all,

Once the tanks have seasoned with age and once you have the plants really going the fish should be doing better as well. Darrell ( @dw1305 ) and Ben ( @Ben Rhau ) know more about plants than me, hope they can help you out.

Just quit on the CO2, rather focus on plants that do well without injection.

Yes, that really. If you have a floating plant it isn't ever CO2 limited and offers a quick response to changing nutrient levels. Have a look at the <"Duckweed Index">.

Observation:This morning, before leaving home, I noticed the fish were swimming near the surface, which is unusual.

That is almost certainly a lack of dissolved oxygen, and that would also account for the deaths.

In fact, I had to direct the filter output towards the glass because my latest addition (a Blue German Ram) didn't like the strong water movement.

That maybe the answer, coupled with chloramine? in the water change water.

Question:Does anyone have any idea what might be causing this issue and what I should do now that the damage is done?

Add some more plants and follow @MacZ 's recommendations?

cheers Darrel

 

[Mike Wise]

Question: does your tap water supply use chlorine to sterilize the water or chloromines? Chloromines do not dissipate by setting it out.

 

[MacZ]

I fogot, I did a quick research, Portugal uses chlorine, not chloramine. And as an EU country the water supplyer is required to make the water analysis pupblic on their website once a year, so the answer will be there.
Darrell, and Mike, if it really was chloramine there would have been more casualties in both tanks.

 

[MacZ]

When I bought this filter, I asked for one that I could use in a larger aquarium in the future, but this came back to bite me because I didn't consider the strong current this filter creates in a small aquarium like mine, which really stresses the fish.

As we are talking canister filters: You can regulate the strength of the flow right at the filter outflow, by putting a valve in the hose. Usually the valves go for only a few bucks. Important is to use the one on the outflo side. I'm using a very old JBL Cristalprofi 700, basically the predecessor of your filter, and do the same. Also I recomment using a spraybar. That way you can tune the current down a lot without losing performance.

Here's an example of said valve. You can also use one by Eheim or Oase, they all fit the hoses.

https://teichbedarf-discount.de/media/image/product/3435/lg/jbl-doppelhahn-schnellkupplung-zum-verbinden-trennen-sowie-absperren-von-schlaeuchen-am-aquarium-o12-16-mm-und-o16-22-mm.jpg

https://ol.nice-cdn.com/upload/image/product/large/default/jbl-cp-absperrhahn-cp120-250-425336-de.jpg

https://media.hornbach.de/hb/packshot/as.46063771.jpg?dvid=8

 

[Mraqualover]

Hi all,


Yes, that really. If you have a floating plant it isn't ever CO2 limited and offers a quick response to changing nutrient levels. Have a look at the <"Duckweed Index">.

That is almost certainly a lack of dissolved oxygen, and that would also account for the deaths.

That maybe the answer, coupled with chloramine? in the water change water.

Add some more plants and follow @MacZ 's recommendations?

cheers Darrel

Hi, thank you for your help. I think there was some confusion. I directed the filter output towards the glass in the rectangular aquarium, but the deaths occurred in the cube aquarium.

 

[Mraqualover]

Question: does your tap water supply use chlorine to sterilize the water or chloromines? Chloromines do not dissipate by setting it out.

MacZ is right; here in Portugal, we use chlorine to treat the water. I read in some Portuguese forums that people who don't have a well and are forced to use public water leave the water out for a few days to let the chlorine dissipate and never have problems. The truth is, I always used well water, and this was the first time I used public water. I left the water to sit, and it got some sunlight, but I doubt that was the issue because there were no deaths in the rectangular tank. Of course, you might say that the fish in that tank are more resilient, but they were also exposed to a larger volume of public water.

Below is a file with the water analysis from my area, just in case you're curious. Apologies for it being in Portuguese. Thank you for your help.

 

[Mraqualover]

As we are talking canister filters: You can regulate the strength of the flow right at the filter outflow, by putting a valve in the hose. Usually the valves go for only a few bucks. Important is to use the one on the outflo side. I'm using a very old JBL Cristalprofi 700, basically the predecessor of your filter, and do the same. Also I recomment using a spraybar. That way you can tune the current down a lot without losing performance.

Here's an example of said valve. You can also use one by Eheim or Oase, they all fit the hoses.

https://teichbedarf-discount.de/media/image/product/3435/lg/jbl-doppelhahn-schnellkupplung-zum-verbinden-trennen-sowie-absperren-von-schlaeuchen-am-aquarium-o12-16-mm-und-o16-22-mm.jpg

https://ol.nice-cdn.com/upload/image/product/large/default/jbl-cp-absperrhahn-cp120-250-425336-de.jpg

https://media.hornbach.de/hb/packshot/as.46063771.jpg?dvid=8

Hi,

I already use the spray bar, but it’s still too strong for the fish. I never used a valve because someone told me, and I don’t know if it’s true, that reducing the outflow with a valve creates pressure inside the filter that could damage it and reduce its lifespan. I will take a look at what you sent, thank you.

Just a quick update: today, after I got home, I saw that all of my fish are still alive, but one of the Rasboras still has the same problem. It keeps its fins closed, almost as if it's curled up, and it looks like it has a sunken belly. I don't know if I should remove it from the aquarium or just leave it there.

 

[MacZ]

I already use the spray bar, but it’s still too strong for the fish. I never used a valve because someone told me, and I don’t know if it’s true, that reducing the outflow with a valve creates pressure inside the filter that could damage it and reduce its lifespan. I will take a look at what you sent, thank you

Of course you shouldn't close it too far, but you can definitely use the outflow valve to reduce the flow from the spraybar. I even got the idea from the manufacturer themselves, they put it in the instructions. You can also take precautions. My best tipp is to use a sponge on the intake. Just put a cyclindrical sponge on it, that way particles are filtered out and the filter doesn't get clogged and flowrates don't go down much. Just remember to regularly clean it.

Below is a file with the water analysis from my area, just in case you're curious. Apologies for it being in Portuguese. Thank you for your help.

Not a problem, many here speak at least some Portuguese and/or Spanish due to connections to Brazil and/or other countries in South America. I speak some Spanish and read Latin, so I can manage.

Not bad readings, btw. Your water is quite good, if it wasn't for the chlorine.

 

[MacZ]

and this was the first time I used public water. I left the water to sit, and it got some sunlight, but I doubt that was the issue because there were no deaths in the rectangular tank. Of course, you might say that the fish in that tank are more resilient, but they were also exposed to a larger volume of public water.

You'ce done everything right, I'm now very sure that was not the cause. And no, the M. ramirezi would have been a sure goner with chlorine, so resilience is relative.