Need Help Diagnosing Fish Health Issues in My 75g Community

About two weeks ago, I set up a new 75-gallon tank after my old one started leaking. While replacing the tank, I temporarily moved all my fish to a 30-gallon tote with a sponge filter. During this time, I noticed one of my platies had developed popeye in one eye, which was also cloudy. After setting up the new tank, I transferred the fish, but the day after the move, I noticed several were breathing heavily, and unfortunately, one died. Their gills appeared slightly enlarged, and some fish had fuzzy fungal growth at the ends of their tails.

I couldn’t tell if the issue was gill disease or flukes, so I treated the entire tank with a combination of Maracyn and ParaCleanse. I planned to wait two weeks before doing a second round of ParaCleanse to target any leftover fluke eggs. Now, a week after the first treatment, I came home to find one of my dwarf gouramis lying at a tilted 45-degree angle on the sandbed. It’s breathing rapidly and looks bloated, as if it has a large ball in its stomach. It occasionally swims up for air, but it struggles to do so.

The other dwarf gourami seems active and is breathing normally, but it has a few missing scales on the top of its head. I’m not sure if this is an injury or something like gourami disease. I haven’t added a new dwarf gourami in six months, but I did have one over a year ago that showed clear signs of gourami disease. I assumed the disease would have died out in the tank by now, but I’m starting to question that.

The platies are also having other issues. In addition to the one with popeye, I’ve noticed their poop is often white or clear and stringy, although it’s sometimes mixed with normal brown poop. One of my platies has a humpback, which it has had since it was a fry. I’ve had this fish for about three months, and I believe it’s genetic, but I’m wondering if it’s humane to keep it living like this.

Some of my female cherry barbs appear bloated as well. This has happened before, so I’m not sure if they’re carrying eggs or if it could be dropsy.

Despite all of this, most of the other fish seem to be behaving normally, with healthy appetites and regular poop. I’m struggling to figure out what’s causing these ongoing problems—whether it’s leftover pathogens from the tote, the new tank setup, or something else entirely. I’d really appreciate any advice or insights into what might be going on. Thanks in advance!

Unfortunately, the dwarf gourami that was lying on the sand has passed. I’ve uploaded pictures showing what it looked like after it passed, as well as the current condition of the other dwarf gourami, which is still alive.

I inspected the bloated gourami closely and didn’t see any signs of pineconing. When I gently touched the bloated area, it felt liquidy and squishy, slightly firm. I’m not sure what this indicates, but I hope the photos will help shed some light on what might have been going on.

The remaining gourami is still active and swimming normally, but I’m keeping a close eye on it for any changes.

Dwarf gouramis (Colisa lalius) and all their colour forms are regularly infected with the Gourami Iridovirus and or Mycobacteria (Fish Tuberculosis, aka Fish TB). There is no cure for either and once those diseases are in your tank, they are there until you disinfect everything including the fish.

The Gourami Iridovirus is a stress virus and causes the fish to develop sores and eventually it suffers from internal organ failure and dies. This takes around 2 weeks from the time the virus first shows symptoms (usually sores on the body).

Fish TB (Mycobacteria) is a slow growing bacteria that normally gets inside fish and settles on organs. It divides and grows over a period of months or years depending on temperature and the size of the fish. It grows slower in cold water and faster in warm water. It kills small fish fast than big fish because it takes fewer bacteria to damage the organs in a small fish due to them having smaller organs to begin with.

The most common symptoms of Fish TB is the fish stops eating, bloats (gets fat) up overnight, does a stringy white poop, breathes heavily/ rapidly at the surface or near a filter outlet, and dies within 24-48 hours of showing these symptoms. Your fish wasn't breathing heavily at the surface and I don't know what the poop was like, but I would say it died from internal organ failure probably caused by Mycobacteria.

The following links have information about Fish TB and includes how it affects people and what you should do if you might have it in your aquariums. I suggest you read them just in case it is Fish TB. The only way to be 100% certain is to have the fish necropsied by a fish vet. Until you can rule out Fish TB, you should avoid getting aquarium water on any open sores/ wounds you have and to wash your hands and arms with warm soapy water after working or do anything in the aquarium.



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Most common livebearers (mollies, platies, swordtails, guppies) from pet shops are regularly infested with intestinal worms. These cause the fish to do eat normally, a stringy white poop, get skinny over a period of time (months). If one fish in your tank has or had intestinal worms, then they all have worms and you can use a deworming medication to treat them. Section 3 of the following link has information about treating intestinal worms.

The platy with the bent back is fine to live its life in an aquarium. In the wild it would get eaten because it can't swim fast enough to get away but in an aquarium where there are no predators, it will happily swim about eating and doing its thing and will be fine. Just don't use it for breeding because it will pass on the deformity to its young.

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The pop-eye (cloudy eye) can be from physical damage to the eye and the fish is putting excess mucous over it until it heals. It doesn't look swollen or sticking out so it's probably just a minor injury that occurred when you moved the fish into the new aquarium. If the water is clean and the eye doesn't get infected, it should clear up on its own in a few days to a week. If it hasn't improved after a week you look at adding medications.

If you do a big (75%) water change and gravel clean the substrate every day (or every second day if you can't do it daily) for a week it should help reduce the number of pathogens in the water and give the fish the best chance of healing its eye. The water changes will also dilute any ammonia, nitrite or nitrate that might be in the water.
*NB* You should test the ammonia, nitrite and nitrate levels in the water because the filter bacteria might have been harmed when you changed tanks.

If there's no improvement in the eye after a few big water changes, add some salt. Salt will help to keep most bacteria and fungus down to low levels so the fish can recover. Salt won't help with Fish TB, there's no cure for that so don't bother wasting your money on so called cures.

See directions below for using salt.

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I wouldn't worry about the cherry barbs unless they stop eating or start to breath heavily.

The fuzzy fungal growth on the ends of the tails of the fish that died shortly after moving could have been excess mucous or Saprolegnia fungus. The fungus gets into damaged tissue and excess mucous is usually produced by the fish if it's injured, and the mucous is used to protect the damage area to help reduce infection. Clean water and salt usually fixes both of these issues.
Excess mucous looks like a cream, white or grey film or patch over part or all of the body.
Saprolegnia fungus looks like white hairs about 3-6mm long sticking up from the area and appears in one location (where there is damaged tissue, a wound).

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Maracyn is an antibiotic (Erythromycin) and should only be used on known bacterial infections. Improper use and mis-use of antibiotics has lead to drug resistant bacteria that kill people, birds, fish, animals and reptiles. Ideally you would have come on here asking for help as soon as the fish started breathing heavily and I would have suggested checking the water for ammonia, nitrite, nitrate and pH, and do a big water change to see if it helped. Too little too late.

The Erythromycin might have wiped out the beneficial filter bacteria in the filter so monitor the ammonia, nitrite and nitrate levels for the next month. If you get an ammonia or nitrite reading above 0ppm, or a nitrate reading above 20ppm, do a 75% water change every day until the levels are 0ppm.

Antibiotics work best in bare tanks with no plants, wood or substrate.
If you use antibiotics or any medication in the aquarium, you should do the following before adding it or re-dosing.

1) Test the water for ammonia, nitrite, nitrate and pH.

2) Wipe the inside of the glass down with a clean fish sponge. This removes the biofilm on the glass and the biofilm will contain lots of harmful bacteria, fungus, protozoans and various other microscopic life forms.

3) Do a 75% water change and gravel clean the substrate. The water change and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in. It also removes a lot of the gunk and this means any medication can work on treating the fish instead of being wasted killing the pathogens in the gunk.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

4) Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use the media. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens so any medication (if needed) will work more effectively on the fish.

4a) Remove carbon from the filter so it doesn't remove the medication from the water. You don't need to remove carbon if you use salt.

5) Increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.

These 5 steps are also used for first aid for fish or if a fish dies. If a fish gets sick you do those 5 steps. The only extra thing you do for first aid is do a 75% water change and gravel clean the substrate every day for a week or until the problem is identified.

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SALT
You can add rock salt (often sold as aquarium salt), swimming pool salt, or any non iodised salt (sodium chloride) to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres (5 gallons) of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for 1 to 2 weeks. If there's no improvement after a week with salt then you stop using it and loot for a broad spectrum medication (preferably not antibiotics).

The salt will not affect the beneficial filter bacteria, fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

When you first add salt, add the salt to a small bucket of tank water (2 litres or 1/2 gallon) and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.

Thank you for your detailed response and all the insights into potential causes, including Fish TB and Iridovirus. The information was very helpful for sorting through what might be happening.

The live gourami still has the patch on its head, but it hasn’t worsened, and the fish swims and eats normally.

A lot of my other fish, like the angelfish and rainbowfish, are still pooping normally (brown and solid). However, the platies continue to have white or clear stringy poop, sometimes mixed with normal brown poop.

I really hope this was Iridovirus rather than Fish TB because the descriptions of Fish TB sound like a nightmare. The gourami that died wasn’t breathing heavily at the surface or showing pineconing, but it was wasting away on the sandbed and very bloated. After the body dried out over night, I noticed that the bloated area released liquid and shriveled up. I’m considering contacting a vet to ask about necropsy services to confirm the cause. Could this possibly have been an early stage of dropsy without pineconing, or was the bloating most likely caused by Iridovirus or Fish TB?

Deworming Plan:
For the platies, should I treat them separately for tapeworms and roundworms using Praziquantel (like PraziPro) and Levamisole (like Expel-P), as the link suggests? I’ve been treating cautiously since I know some meds are specific to certain worms.

Other Notes:

• The platy with the humpback is doing fine, which is a relief. I don’t think breeding would be an issue because fry would likely get eaten by the larger fish.
• The platy with popeye has had it since I changed tanks about two weeks ago. It’s only in one eye, which makes me think it’s an injury.
• I tested the water with an API test kit, and there was no ammonia or nitrite. Nitrates are about 5–10 ppm.
• I’ll follow your advice to do 75% water changes and siphon the sand daily for a week to see if there’s any improvement. If nothing changes, could I move the platy to a quarantine tank and use salt there since my plants don’t tolerate salt.
• I forgot to mention that while setting up the new tank, one of the gouramis had died inside the tote. Since it was the only fish that died while inside the tote, and I originally had three but now only have one left, I think it’s more likely to be gourami disease.

The remaining females (cherry barbs) are eating and swimming normally despite looking bloated. This has happened multiple times in the past after the barbs display breeding behaviors, but I’ll also monitor them closely for any changes.

Background Context (Before the Leak):
About a month ago, I received a new group of fish for my tanks: dwarf neon rainbowfish, rummy nose tetras, emperor tetras, and dwarf gouramis. They were placed in either my main or quarantine tank. Shortly after arrival, some of the fish started showing symptoms like red gills, bloating, and rapid breathing. Others showed swim bladder issues or fin rot.

I treated with PraziPro in both tanks for flukes and tapeworms, which helped resolve the symptoms after 1-3 weeks. Most of the fish recovered and were healthy when the tank leak occurred. Unfortunately, I lost several fish during that time, including some of the new rummy nose tetras and one Boesemani rainbowfish from my main tank with enlarged gills.

The fish I purchased then that I had moved in my quarantine tank, have shown no issues so far and appear perfectly healthy. I plan to keep them there until the main tank is stable and all problems are resolved.

Post a picture of the gourami with the patch on its head.

Re the gourami that died, it could be dropsy but could be TB. I would assume the worse and work on that just in case it is TB. Dropsy doesn't always cause the scales to stick out and is normally caused by internal organ failure whereby one or more organs have been damaged by physical injury or something else (virus or bacteria). Where the organ ruptures the abdominal cavity fills with fluid and the fish bloat up and die.

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If you can get a deworming medication called Flubendazole, it will treat round and flat worms at the same time and you only need to use one medication. If you can't get Flubendazole then treat the fish for round worms first (use Levamisole).

If you used PraziPro on all the fish tanks when you used it a month ago, then they should be free of tapeworm and you shouldn't need to treat them again for that. However, if you didn't treat them all with PraziPro, then you will need some Praziquantel (preferably on its own and not mixed with anything else) to treat all the fish for tapeworm and gill flukes.

When you deworm fish, you need to treat all the fish and all aquariums at the same time to prevent cross contamination.

You should also disinfect any nets, buckets and gravel cleaners to kill anything on them. Plastic containers can be bleached for 15-30 minutes and rinsed with tap water. Nets can be washed in hot soapy water, rinsed and left to dry.

Make sure there is no carbon in the filter when deworming the fish because it will remove the medication.

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Plants will normally tolerate the salt level for treating minor infections but if you are concerned then yes you can move the platy with the cloudy eye into a spare tank to treat with salt.

Use water from the tank with the platy to set up the new tank.

When you catch the fish, try not to lift it out of water in the net. Catch it in a net and keep it in the water, then put a plastic container in the water under the net and lift the fish up in the net in the water. This will reduce the risk of the fish getting more damage from the net and being lifted out of water.

I’ll send a picture of the gourami with the patch on its head soon, and I’ll check with my vet tomorrow to see if they can do a necropsy on the one that passed.

Regarding deworming, I can order Absolute Wormer Plus, which has flubendazole as the main ingredient, and it would arrive by Tuesday. I like that it treats both roundworms and flatworms at the same time. Alternatively, I could pick up Expel-P (levamisole) from my local fish store if it’s more urgent to treat for roundworms first. However, by the time you read this, I’ve probably already ordered the flubendazole since it seems better to cover both types of worms, also since parasites tend to act slowly.

I’ll set up a 5-gallon quarantine tank tomorrow for the platy with popeye. I’ll add salt initially and start the medication as soon as I have it. I’ll also make sure to disinfect all my nets, buckets, and tools as you suggested to avoid cross-contamination, along with the daily siphoning.

Intestinal worms don't kill fish quickly and most fish carry some all the time. Just get the Flubendazole based medication and use that when it arrives. You might have to work out the amount of medication, I don't know if they have dose rates on the packaging for fish. I'm no good at maths so if you do need to work out the amount, start a new thread and ask online here. There are a few people on the forum that are good with formulas and dose rates.

To help prolong the lives of fish infested with intestinal worms, you can feed the fish more often (3-5 times a day) until they get treated for worms and also for a month after they have been treated. The worms suck the blood out of the fish and feeding the fish more often allows them to make more blood so they don't die as quickly from lack of blood. And feeding them more for a month after they were treated helps the fish regain some body mass quicker.

Do more frequent water changes, gravel cleans and filter maintenance if/ when you feed more often to keep the tank clean.

This will pass, with the kind of advice above. You then you look longer term, and lock into disease prevention mode. That's not always easy, as most of the health problems we see come from the supply chain - the farms.
In a perfect aquarium set up, you'll have a quarantine tank, set up like a permanent tank but used for new arrivals for several weeks. It's a fine idea, but not many people really do it. It can save you enormous problems.
Then you need to look at stocking. An overstocked tank is a time bomb. You sound like you have a lot of fish there.
Finally, most importantly, you need a regular as clockwork water change regime. With most tanks, 25 to 30% a week is ideal. It's the walking the dog on a cold morning side of fishkeeping.

I recently dosed Flubendazole in all my tanks to treat for internal parasites. Right now, about 90% of my fish are displaying stringy white poop in the 75g, but that’s the only symptom. Should I redose in a week and continue for the full four-week treatment as advised in the forum? Additionally, should I do a 75% water change and filter cleaning two days after the first dose? I want to make sure I’m following the process correctly.

Just a reminder:

About a month ago, I purchased new fish, including emperor tetras, rummy nose tetras, and dwarf gouramis. I quarantined them for two weeks in a 20-gallon tank and treated them with the med trio (ParaCleanse, Maracyn, and Ich-X). They appeared healthy by the end of the quarantine, so I added some of them to my main tank.

Two weeks ago, my 75-gallon tank started leaking, and I had to move all the fish into a 30-gallon tote with a sponge filter. I did water changes and dosed with Seachem Prime to detoxify ammonia, which stayed at 0 the entire time, but there was gunk on the bottom. Unfortunately, one dwarf gourami died in the tote. After setting up a new 75-gallon tank and transferring the fish, more problems started.

While water parameters in the new tank have been perfect, the 3 gouramis have been particularly affected. I suspect Iridovirus, as they’re the only species showing severe symptoms or dying. I also contacted local vets, but none in my area offer necropsy services.

To prevent cross-contamination, I’ve been treating all my tanks, including the 20-gallon quarantine, with Flubendazole. Alongside the treatment, I’ve been performing daily gravel vacuuming and water changes in the 75-gallon tank to maintain water quality. My tank is slightly understocked now because a few months ago, my angelfish ate a school of neon tetras. I plan to replace the angelfish with a juvenile pair to raise them alongside the tetras and avoid future predation.

The platy with popeye has almost fully recovered in a 5-gallon quarantine tank after being treated with salt, only one of its eyes looks cloudy but it has gotten better.

My last remaining dwarf gourami is improving; the faint/discolored patch on its head is barely visible now, and it eats and swims normally.

The emperor tetras and rummy nose tetras in the 20-gallon quarantine are also doing well since I've kept them, with no signs of illness.

I’ll upload pictures I took five days ago of the gourami that was previously affected—apologies for the delay in sharing them. Let me know if I need to continue daily gravel vacuuming or take any additional steps. Your advice would be greatly appreciated. Thank you!

You should deworm the fish once a week for 3 to 4 weeks so you kill any baby worms that hatch after the first treatment.

You should do a 75-90% water change and gravel clean the substrate, and clean the filter 24-48 hours after each treatment. The water change removes the medication so you don't overdose when you do the next treatment. The water change and gravel clean remove expelled worms and worm eggs from the water and substrate, and so does cleaning the filter.

Make sure there's no carbon in the filter when using medications

Increase aeration/ surface turbulence when using medications.

Quick update! The flubendazole seems to be working following your instructions. All the fish are looking better, and their poop is solid and brown now, which is good.
Also, the gourami is in perfect condition and has healed entirely somehow. I still don't know what the little guy had though so I'm a bit confused about how it happened.

But yesterday, the platy with popeye I moved back from the QT tank about a week ago died. Its eye looked totally messed up, like it was rotted away when I found the body. I didn't notice it until I found it dead at the back of the tank doing a wc. Then today, one of my otos died too—mouth rot or some kind of fungus. There’s one other oto with the same thing, but it’s still alive. All the other fish seem fine, just that one sick oto now.

So I’m wondering—should I add salt to the tank? I’m kinda thinking it might be columnaris since it spread pretty fast and there was fungus. Also, could I use Kanaplex (kanamycin) to treat it? If so, do you recommend I mix it into food or just add it straight to the water?

Still currently have a week left on the flubendazole treatment, btw. I attached some pics of that oto too. What do you think?

Did you take any pictures of the dead platy and Otocinclus?

What is the ammonia, nitrite, nitrate and pH of the water?

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Mouth fungus (aka Columnaris) is a fast growing flesh eating bacteria that appears as white on the mouth and rapidly (within 24-48 hours) spreads over the face and head. The fish usually dies within 24-48 hours of symptoms first appearing. I have never heard or seen it affect Otocinclus but that doesn't mean it can't.

The catfish has very red gills and that could indicate a water quality issue or an infection in the gills.

The white stuff on the nose is excess mucous produced by the fish to protect an injured area (bump on the nose, etc). It will also appear like that for Columnaris.

Columnaris is normally introduced into an aquarium with sick fish or contaminated water. If you haven't added anything new to the tank in the last few weeks, it is unlikely to be Columnaris. You have also been doing big regular water changes and that helps prevent this disease from occurring.

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You can try adding salt to the tank. Use 2 heaped tablespoons per 20 litres (5 gallons) and keep it in there for 2 weeks. If there's no improvement after a few days, post more pictures.

If you want to use Kanaplex, try to use it in a bare tank so it works on the fish and not the bacteria in the main display tank. You can move a rock and a few plants into the treatment tank for the Otocinclus to feed on while it's being treated.

No, I didn’t get any pictures, but I’ll go ahead and add the salt as you suggested. I haven’t added anything new to the tank recently either.

The oto that died had really severe damage when I found the body—a portion its face was gone, from the mouth up to the eyes, covered in fungus. It didn't look as bad the night before, just like the one that’s still alive now.

Tank parameters are all good: 0 ammonia, 0 nitrite, 0-5ppm nitrate, and pH is 7. I’ve been consistent with the water changes and always vacuum the substrate thoroughly, especially under the wood since that's where most the poop is.

If anything changes or spreads, I’ll update

Quick question: do I need to bleach my aquarium equipment between water changes during deworming treatment? So far, I’ve been using bleach to disinfect my siphon, hoses, and nets every week of treatment, but I just ran out. I’m about to do a water change and realized I should’ve asked earlier: Would worms or parasites survive on equipment like the siphon/hoses or nets while they’re drying outside the tank? Should I continue bleaching in between changes for future cases of breakouts?

Also, for my separate quarantine tank, which is empty now but previously held the platy, do I need to disinfect it as well? Or will leaving it to dry out be enough?

The separate quarantine tank should be washed out and cleaned, then left to dry. You can use bleach or white vinegar to clean the aquarium. Vinegar is safer for the silicon. If you use bleach only leave it in contact with the silicon for 10-15 minutes and then rinse it out.

Use bleach outdoors or in a well ventilated area.

Wear rubber gloves and safety glasses when working with bleach.

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You don't normally have to bleach nets and containers after each deworming treatment. Normally letting them dry properly will kill most parasites and diseases that live in water. I used to rinse the stuff down with tap water after use then let it dry for a few days. If you can leave it in the sunlight for a few hours that will kill most things too. Mid-day sun is the best for this.