Help! Moderate/severe fin rot

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Aquarium Advice Newbie
Jun 14, 2023
My question is should I use tetra lifeguard to treat fin rot and how much? My two gold fish were in a 10 gallon, it needed to be cleaned, but also they needed a larger tank. I had just treated them for ich, or what do I thought was ick. Stupidly we got them a 20 gallon tank put them in it without cycling it. Within 24 hours they were covered in white fluffy/ stringy stuff, which maybe was Cotton fin. I thought the ich treatment would kill this and gave another dose even though I had just finished three days of medication days before because I realized I had been under medicating. Instead of 1 drop per gallon, I gave them 1 for every 2 gallons. By morning my black moor goldfish was dead., But my regular gold fish was still alive. I moved him to a smaller 4 gallon tank that I believe has been cycled, ( plant that was in it had been growing for a couple months)( we took out the plant and put it in the new bigger tank). I added 3/4 tablespoon of aquarium salt to tank and the white stuff on my fish started coming off. Most of it is gone, just two small dots on face and some still on his eyes. However, i can now see that my fish has moderate, soon to be severe fin rot. He also hasn't eaten for the last several days. He also has pooped a lot, until it was just clear stuff coming out. I got a 3 Gallon tank bubbler and put it in. When something hit his mouth, he ate it, so I think he is hungry , but can't see the food to eat it. He still has enough energy that I can't catch him to syringe feed him. He was up and swimming around yesterday, but is now sitting at the bottom of the tank today and the fin rot looks like it's getting worse. So question is should I give him lifeguard and should I give the whole tab that's for 5 gallons when it is a four gallon tank? Also as far as I can see the parameters look good, but I haven't tested ammonia levels. temp is 74 degrees, I am trying to lower it to 72.
Hi and welcome to the forum :)

Goldfish don't normally get white spot and if you haven't added any new fish to their tank in the last few weeks, it is unlikely to be white spot.

When fish are stressed by something in the water, they produce extra mucous over their body and fins. This can appear as a cream, white or grey film over part or all of the body and fins. If you moved the fish into a new tank and they developed excess mucous within 24 hours of going into that tank, then something in the tank is poisoning them. The best solution is a big water change every day for a week, or moving them back to their original tank.
When doing water changes, make sure any new water is free of chlorine/ chloramine before it's added to the tank.

If you can provide some pictures of the fish (dead and alive), we might be able to offer more info. But my guess is they have been poisoned by something in the new tank.

If you can test the water for ammonia, nitrite, nitrate and pH, post the numbers here.

Dropping the temperature isn't going to make any difference.
The nitrite and nitrate levels appear to be zero, the ph is around 7-7.5. I don't know the ammonia levels. I did a 25% water change and that seemed to perk him up for a few minutes.


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I took him out of the new tank and put him in an extra tank we set up a couple months ago with a plant. I read that if the plant shows new growth then the tank has cycled. so, he should be in a clean cycled tank now. I put aquarium salt in the tank and mist if the white stuff came off, he was swimming around , but now just hangs out at the bottom with his butt floating higher than the rest of his body.
Plant growth has nothing to do with being cycled. In fact you would probably see better plant growth in an uncycled tank because the plants would be feeding on nutrient inbalances. The only way to see if a tank is cycled is if you consistently see zero ammonia and nitrite in a tank that has ammonia going into it. Either ammonia from fish waste or dosed ammonia.

A 4g tank is far too small to keep a goldfish in. You might get away with it for a week or 2, but it can take months to cycle the larger tank and being in such a small tank for that long will cause long term health issues in a goldfish. It would be much better to have the goldfish in 20g, even if the 20g isnt cycled, as long you keep up with enough water changes to maintain water quality until it cycles. I would go as far as say a 4g tank, with such a large, messy fish as a goldfish just simply isnt big enough to cycle.

Do you know how to cycle a tank with fish?
The white patchy stuff on the fins and body is excess mucous.
The red areas on the fins is blood.
I would say the fish is suffering from ammonia poisoning or some other sort of poisoning.

Treatment involves big (75%) water changes and gravel cleaning the substrate every day for a few weeks. Then every second day for a few weeks. You should also reduce feeding to 2-3 times a week. Don't worry, the fish won't starve. But the less food going in, the less ammonia produced by the fish.
Right now he's not eating. The pictures aren't the best for showing the fin rot. His fins have their shape, but are shredded.
No I don't fully know how to cycle a tank with a fish. In the past we just put him in the tank and let it do it's thing.
To cycle a tank you need to grow denitrifying bacteria to consume ammonia and nitrite that your tank produces. The bacteria needs an ammonia source to grow colonies sufficient in size to consume all the ammonia and resultant nitrite and turn it into nitrate which typically you remove through your regular water changes.

A fish in cycle uses fish waste as an ammonia source and regular water changes are undertaken to ensure that water parameters are maintained at relatively non toxic levels.

Set up your tank. Make sure everything is running smoothly. Make sure you have used a water conditioner product with any tap water you have put in your tank. Seachem Prime is a water conditioner that will also detoxify some ammonia for a day or two, so is a good choice for a water conditioner while cycling a tank with fish.

You should have a test kit. Preferably a liquid test kit. It should test for ammonia, nitrite, and nitrate.

In ideal circumstances you should be starting a fishless cycle with a low bioload (number of fish). 1 small fish per 10 gallons/40 litres is a good number of fish, but this can be tweaked a little for fish that are social and don’t do well on their own. Ideally a hardy type of fish. You may have fully stocked (or overstocked) your tank before you knew about cycling. In these circumstances, if its not possible to return fish, you will have to make the best of it.

If you haven’t already done so, add your fish. Acclimate them to the water in your tank before doing so.

Feed lightly to start with. Daily as much as is eaten in 2 minutes, or as much as is eaten in 3 minutes every 2 days. You can increase to full feedings if you are confident your parameters aren’t getting too elevated too quickly and water changes don’t become a daily thing.

Start to regularly test the water for ammonia and nitrite. At least daily. Depending on your bioload you could start to see ammonia quite quickly. Nitrite will likely take a little longer to appear.

Your target should be to keep ammonia + nitrite combined no higher than 0.5ppm by changing water whenever your water parameters exceed this target. 0.5ppm combined is a level of waste that is sufficient for your cycle to establish but relatively safe for your fish.

If you see 0.5ppm ammonia and 0.0ppm nitrite (0.5ppm combined) then leave things be. If you see 0.5ppm ammonia and 0.25ppm nitrite (0.75ppm combined) then change 1/3 of the water. If you see 0.25ppm ammonia and 0.75ppm nitrite (1.0ppm combined) then change 1/2 the water. If water parameters get worse than these levels it may require multiple daily 50% water changes to maintain safe water conditions. This is more likely to happen with a fully stocked tank.

Remember to add water conditioner whenever you put tap water in the tank.

Over time the frequency of water changes and amount you need to change to maintain your ammonia + nitrite combined target will reduce. You can also start testing for nitrate and should see this rising. If you are finding the ammonia and nitrite in your tests are consistently low, and you aren’t already fully stocked, you can add a few more fish. It may take a few weeks to get to this point.

Once you add a few more fish, continue to regularly test the water and continue to change water if you exceed the 0.5ppm combined ammonia + nitrite target. With added bioload the frequency of water changes and amount you need to change may increase again until your cycle has caught up. Again once you are consistently seeing low ammonia and nitrite you can add some more fish. Rinse and repeat with testing, water changes, and adding fish when safe to do so until you are fully stocked.

You can then cut back on water changes to control nitrate only. Typically you want to keep nitrate no higher than 40ppm, but I would recommend changing some water every 2 weeks even if your water test says you don’t need to.

A fish in cycle from an empty tank to fully stocked can take several months.

A good way to speed up this process would be to put a small amount of filter media from an established filter into your filter, or get a sponge from an established filter and squeeze it into your tank water. Perhaps you have a friend who keeps fish who could let you have some? This will seed your filter with the bacteria you are trying to grow and speed up the process.

Another option is bottled bacteria like Dr Tims One + Only or Tetra Safestart. These products wont instantly cycle a tank as they claim but in a similar manner to adding established filter media they can seed your filter with the bacteria you are trying to grow to establish your cycle. These products are hit and miss as to whether they work at all, but are an option if established filter media isnt obtainable and may speed up the process from several months to several weeks.
To add to above i would recommend moving the fish to the bigger tank and cycling that. A 4g tank will be impossible to cycle safely with a goldfish in there.
Also, what should I do about the fin rot? His tail and fin shape is still there, but they're shredded looking. Should I give him the lifeguard?
Also, what should I do about the fin rot? His tail and fin shape is still there, but they're shredded looking. Should I give him the lifeguard?

Big (75%) daily water changes and salt should help with the fin rot.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.


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 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 at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

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.

When 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 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.
We moved him back to the old tank and checking morning and night for the ammonia and nitrite levels. My fish is looking better, but his eye still has the white cottony fungus on it. My biggest concern now is that he still not eating. It is now day 5 since he stopped eating. He is swimming and resting a lot with his fins erect. I think I was stressing him out watching him so intently to see if the fin rot has stopped progressing, he seems more calm now that I'm not right at his tank.
The white stuff around the body is excess mucous produced by the fish to protect the damaged tissue. Keep the tank clean and have some salt in it. Don't stress the fish and give it time to recover. Fish can go for weeks without food and not starve, so just keep it clean and when the fish has recovered from the poisoning, it should start to eat again. If you add some live aquatic plants, the fish can eat them if it gets hungry. But right now it needs time to recover.

Thank you for everyone's advice. He is eating again, swimming around his tank doing normal fishy things. We got him an air stone which he seems to really enjoy. His fins are starting to grow back and his eye looks better every day. Some of his scales turned black, which I read is part of the healing process from an ammonia burn. We've had this guy for 7 years and have never had a problem with ammonia poisoning or burns, he's a tough fish, but we have had fancy goldfish die out of the blue several times, probably from ammonia poisoning. Thank you again, the salt fixed everything. We'll definitely be better at monitoring the ammonia levels.
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