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New betta fish sick: fuzzy fungus, lying on bottom. How to save him?

Updated on September 23rd, 2025

Pet's info: Fish | Unknown - Fish | Male

Hello! I purchased a male koi betta from a Petco two days ago. He is currently living in a two gallon filtered aquarium. Yesterday I noticed him laying on the floor of the aquarium, but I assumed he was just sleeping. Today when I woke up he was covered in a sort of fuzzy substance, which I assume to be fungus, and still laying on the floor of the aquarium. Sometimes he will get up and swim around. I want to do something to prevent him from dying, but I don't know what to do. Please help!

3 Answers

Most Helpful Answer

Angel Alvarado, LVT

Answered By Angel Alvarado, LVT

Licensed Veterinary Technician

Published on June 16th, 2017

If you set up your tank and added Cola the same day, it is likely you are having water chemistry issues in addition to a fungal infection. Tanks should be set up and run for about 4 weeks before adding fish. This allows the tank to cycle. This means beneficial bacteria will populate the filter and substrate. It is important because they rid the tank of toxins such as ammomnia and nitrites.
Since he is in the tanlk already, you can use a quick start product to jump start the nitrogen cycle. You can purchase this at the pet store. You will also need an antifungal medication. Follow label directions carefully.
Make sure water temp is between 78 and 82 F and use a low flow filter to prevent a strong current. Partial water changes (no more than 30%) may be necessary to reduce ammonia and nitrite levels until the tank has cycled. Used aged or conditioned water that is temperature matched.
Vote Icon1Pet Parents found this answer helpful

Related Answers from Veterinarians

  • Answered By Angel Alvarado, LVT

    Licensed Veterinary Technician

    Published on July 25th, 2018

    It could be some fin rot and fungus growth. The foundation for treatment and recovery is pristine water. You can use a home test kit or submit a water sample to confirm proper chemistry. Most pet stores will do this for free or for a small fee. Aim for 0 ppm ammonia, 0 ppm nitrites and 20 ppm or less nitrates. Perform a partial water change if indicated. Use aged or conditioned water that is temperature matched to prevent further stress or shock. Do this every few days to maintain water quality. To treat the fungal infection, you'll need a product such as Fungus Cure (API) or LifeGuard All In One (Tetra) . You can find them in the Aquarium section of the local Petco. Follow label directions and remove the carbon filter insert during treatment.
    Water changes and medication should resolve the infection in a week or two. The fins should slowly heal up afterwards. Perform regular testing and partial water changes to keep the tank clean. Remove any uneaten food to prevent fouling the water. Feed a high quality, high protein pelleted diet. Hikari makes several types. You can find them at Petco as well.

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    1Pet Parents found this answer helpful

  • Answered By Andrea M. Brodie, DVM

    Veterinarian

    Published on November 18th, 2018

    He has to get used to his home. Moving him to a new tank can be stressful. Fish can handle not eating for up to two weeks, so there is no big worry yet,
    Make sure his water temperature is adequately warm. If the water is too cold, he will not be hungry. Check water chemistry using a home test kit or by submitting a water sample for testing. Aim for 0 ppm ammonia and nitrites with a 40ppm or less nitrate level. Perform partial water changes to stabilize chemistry and maintain water quality. Use only aged or conditioned water that is temperature matched to prevent stress or shock. A bit of aquarium salt (NOT table or Epsom salt) can be used as a general tonic to reduce stress, treat minor infection and aid in any recovery. Dissolve 1 teaspoon of salt per gallon of water in a cup of tank water and gently pour it into the tank.

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    1Pet Parents found this answer helpful

Smart Picks for Smart Questions

Health & Wellness
My betta has white spots, not responding to ich meds. Is it fungus?
It doesn't have the appearance of ich. He would have white spots, like grains of salt all over him. I don't see fungal growth either in the images. He does have some fin rot though. Check the water chemistry. Use a home test kit or submit a water sample for testing. Most pet stores will do this for free or for a small fee. Confirm an absence (0 ppm) of ammonia and nitrites with nitrates at 40 ppm or less. maintain temp between 78 F and 80 F. This is the optimal range for a Betta. Maintain pristine water quality as well as temperature. Continue with the ParaGuard since it is appropriate for fin rot. Follow label directions. You can also add in a bit of plain aquarium salt (NOT table or Epsom salt) as a general tonic to decrease stress, improve gill function, treat minor infection and aid in recovery. Dissolve no more than 1 teaspoon of salt per gallon of water in a cup of tank water and gently pour it into the tan. Treat with salt for 10-14 days then reassess his condition. Partial water changes can be done to reduce salinity. Use only aged or conditioned water that is temperature matched to prevent stress or shock. You may need to treat the fin rot for longer but don't use salt for more than 2 weeks in a row without a break. Also, if possible, decrease filter flow to reduce the current. Bettas prefer slow moving water. To provide an immune system boost, you can soak pellets in some garlic juice .
Updated on September 23rd, 2025
Food & Nutrition
Why is my Betta fish's tail fuzzy and she won't eat or move?
This could be either a bacterial infection, such as Columnaris, or a fungal infection, such as Saprolegnia. It is difficult to say without an exam or image. Either can be treated with medications found in the aquarium section of the local Petco. Look for an antifungal or antibiotic. You may even find a combination product. Follow label directions carefully and remove the carbon filter insert during treatment. Maintain pristine water quality via filtration and regular partial water changes. If an antifungal does not work, try an antibiotic or vice versa. Keep water temp between 78 F and 80 F.
Updated on September 23rd, 2025
Health & Wellness
My old Betta fish has white spots and is hiding. How can I treat him?
Maintain pristine water quality via filtration and regular partial water changes. Use only conditioned water that is temperature matched to prevent further stress or shock. Bettas do best between 78 F and 80 F. You can try an "all in one" product, such as Lifeguard by Tetra, to treat the condition. Find it in the local Petco or online. Follow label directions carefully and remove the carbon filter insert if indicated. https://www.petco.com/shop/en/petcostore/product/tetra-lifeguard-all-in-one-freshwater-aquarium-treatment
Updated on September 23rd, 2025
Food & Nutrition
Why is my Betta fish lying on its side, has foggy eyes, and can't swim?
He is "old" for a Betta. Check the water chemistry and temperature. You can use a home test kit or submit a water sample for testing. The local Petco may do this for free or for a small fee. Aim for an absence (0 ppm) of ammonia and nitrites with nitrates at 20ppm or less. Perform partial water changes to stabilize chemistry and/or to improve water quality. Use only conditioned water that is temperature matched to prevent stress or shock. Bettas do best between 78 F and 80 F. The cloudy eyes may be due to infection. Maintaining pristine water quality will help, but you may need a broad spectrum antibiotic as well. Look in the aquarium section of the local Petco for medication. Follow label directions carefully and remove the carbon filter insert during treatment if indicated. Even with treatment, there may be permanent damage to the eyes if the condition has been chronic. The "laying down" is sometimes seen even in healthy fish. They may choose to lay on gravel or the broad leaf of a plant. It may also indicate infection or injury though. If hebisbhavibg difficulty reaching the surface, decrease the water level to make it easier. Bettas need to surface occasionally to get some air.
Updated on September 23rd, 2025
Vet Q & A
Why is my betta struggling to swim with a curved spine and gasping?
Recheck water chemistry to confirm 0 ppm ammonia and nitrites with nitrates at 20 ppm or less. A pH of 7 is fine and they can adjust to more acidic water as long as the change is gradual. Temperature should range between 78 F and 80 F. Plain aquarium salt (NOT table salt or epsom salt) can be used as a general tonic to reduce stress, improve gill function, treat minor infection and aid in recovery. Dissolve 1 teaspoon of salt per gallon of water in a cup or two of tank water and gently pour it into the tank. Perform partial water changes every couple of days to maintain water quality. Treat only the volume of water being replaced. Treat with aquarium salt for no more than 14 days then reassess the condition. An antibiotic, such as kanamycin or erythromycin, can be found in the aquarium section of the local Petco if the salt treatment doesn't help. Follow label directions carefully and remove the carbon filter insert during treatment if indicated.
Updated on September 23rd, 2025
Vet Q & A
My goldfish has a fuzzy white growth. Is it fungus? How do I treat it?
If it is fuzzy, it is likely fungal. You can try with a commercial antifungal medication such as API Fungal Cure, methylene blue or Pimafix/Melafix. These can be purchased online or in the aquarium section of most pet stores. Read package directions carefully and remove the carbon insert from the filter before treatment if indicated. Plain aquarium salt (NOT table salt) can be used in conjunction with one of the above treatments to aid healing. Dissolve up to one tablespoon per gallon of water into the tank. Fungal infections can take up to two weeks to resolve with treatment. Maintain proper water parameters (0 ppm ammonia/nitrites, 40ppm or less nitrates and temp of 65 F to 72 F). If possible, remove the affected fish yo a hospital tank during treatment.
Updated on September 23rd, 2025
Vet Q & A
Why are my fish slow and weak from a fungal infection in the tank?
Fungal infections are usually due to poor water quality. Check the water chemistry, change or rinse filter media, perform a partial water change (use aged or conditioned water that is temperature matched to prevent shock) and treat with an antifungal until the condition clears. You can find an antifungal in the aquarium section of most pet stores. Follow label directions carefully.
Updated on September 23rd, 2025

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