My goldfish has brown spots and it's getting worse. What to do?
Updated On September 23rd, 2025
Hello, we have a fan tail goldfish and it’s getting brown spots/splotches all over him. I’ve changed the water in the tank already and added the ammonia detoxifier. It seems like it’s getting worse.
2 Answers
Most Helpful Answer
Published on August 21st, 2018
This could be ammonia burn. Check the water chemistry. 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 a nitrate level of 20 ppm or less. Partial water changes will be needed to stabilize chemistry. Use only aged or conditioned water that is temperature matched to prevent further stress or shock. Goldfish are cold water fish and do best between 65 F and 72 F. When using an ammonia reducing product, be sure to test the water after treatment but before pouring the treated water into the tank.
1Pet Parents found this answer helpful
Related Answers from Veterinarians
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Published on July 8th, 2017
The brown marks are likely diatom growth. You can rid the tank of them by confirming or providing adequate filtration, increasing water motion (use powerheads to create current), remove any tank furniture and scrub with a stiff brush or bleach it, perform a 30-50% water change before returning tank furniture, regulate light exposure (use a timer on tank lights), repeat this process every 2 weeks. You will see less diatom growth after each cleaning. If possible, consider moving the goldfish into a larger tank, at least 75 gallons if you have the space.
1Pet Parents found this answer helpful
Health & Wellbeing
I had put an aquatic plant in my fish tank because I was told he would like it and eat it, but now he has black marks all over his body. I searched and found that it is chemical burns from ammonia due to the plant. How can I help get rid of the
The ammonia spike was likely a result of decaying plant matter. As long as you maintain pristine water quality, Goldilocks should heal. Use a filter that is rated for at least twice the volume of the tank. Since goldfish produce a larger than average bio-load (waste), you may need to perform partial water changes regularly in addition to filtration. Use only conditioned water that is temperature matched to prevent stress or shock. Goldfish are cold water fish and do best between 65 F and 72 F. Use an additive, such as Stress Coat, to promote healing. A home test kit should also be used to monitor chemistry. Aim for an absence (0 ppm) of ammonia and nitrites with nitrates at 20ppm or less. If you don't have a teat kit, the local Petco may test water for free or for a small fee.
Updated on September 24th, 2025
Health & Wellbeing
My gold fish got white spots on her fins and body and she has got red spots also. The white thing looks like fungus. 7 of my fishes died due to this. They became slow and just sat down and slowly died. Just one left plzz help. What can I do?
This problem could be due to a fungal or bacterial infection, but certainly a more radical approach is required. Begin by submitting a water sample for quality testing. Most pet stores will do this for free or a nominal fee. Clinical examination should always include a water quality check, even if you have done so already. Water testing should be performed with a quality test kit, measuring NH4, NO2 and NO3. High ammonia levels, PH imbalances may be responsible for these signs. Oxygen concentration and quality of the filters should be determined as well. If water quality is good and there are no major imbalances, your fish should get examined to look for any sign of bacterial/fungal infection and eventually water should be treated. Hope this answer was helpful, but please do not hesitate to contact us again on the forum or by requesting a consultation if you have any more questions or to discuss it any further.
Updated on September 24th, 2025
Health & Wellbeing
My goldfish's fins are turning black. I changed the whole water 2 days back. I put medicine after every water change. Still it's increasing. What should I do? And how often should I change the water and amount of water I should change? Can we substi
Elevated ammonia levels can result in "burns" which may turn fins and scales black. Use a home test kit or submit a water sample for testing. Most pet or fish stores will do this for free or for a nominal fee. If ammonia levels are elevated, daily partial water changes, using aged or conditioned water, can decrease ammonia to safe levels (0.25 ppm or less).
StressCoat or plain aquarium salt (NOT table salt) can aid in healing. Dissolve 1 teaspoon of salt per gallon of water into a cup of tank water and gently pour it into the tank. Confirm adequate filtration. The filter should be rated for at least twice the volume of the tank.
You can change 20-30% of the tank water every couple of weeks. Use only aged or conditioned water that is temperature matched to prevent stress or shock.
Updated on September 24th, 2025
Health & Wellbeing
First and foremost, my tank was very dirty. So dirty to the point that one of my goldfish was turning a brownish- black color. The other one seemed alright. When I did a 100% water change I saw a fuzzy white streak on its body that turned out to be f
It may have been her slime coat coming off. The black color could have been caused by high ammonia levels. It can cause "burns" which will discolor scales.
In the future, it is best to perform 30-50% water changes daily to balance chemistry and improve water quality. Use only aged or conditioned water that is temperature matched to prevent further stress or shock. Your filter should be rated to handle at least twice the water volume of the tank.
Updated on September 24th, 2025
Health & Wellbeing
hi. my gold fish has big red spot on her body. it looks like burbles and it seems that she is sick. what can I do for her?
Those may be small hemorrhages and your gold fish may be suffering from a systemic infection (potentially bacterial). The approach to this problem must be radical and logic. Begin by submitting a water sample for quality testing. Most pet stores will do this for free or a nominal fee. High ammonia levels, PH imbalances may be responsible for that. Oxygen concentration and quality of the filters should be determined as well. If water quality is good and there are no major imbalances, your fish should be treated with antibiotics. Please do not hesitate to contact us again on the forum or by requesting a consultation if you have any more questions or to discuss it any further.
Updated on September 24th, 2025
Health & Wellbeing
Hello, I have 2 goldfish who recently had a pleco added to their tank. A week after one of the goldfish had red spots all over. Being concerned we removed the pleco but the goldfish is still showing symptoms. I did a complete water change adding anti
Check the water chemistry. Two goldfish can quickly overwhelm a tank with their large bio load. Aim for 0.25 ppm (parts per million) or less ammonia, 0 ppm nitrites and 40 ppm or less nitrates with a temp between 65 and 72F. If water chemistry is good, it is possible the red marks are from the pleco. They are notorious for sucking the slime coat off goldfish leaving red marks and wounds. Partial water changes, 30-50%, using aged or conditioned water that is temperature matched are safer and less stressful than complete changes. Give the antibiotics time to work. You can add in plain aquarium salt (NOT table salt) to aid healing. Dissolve one teaspoon per gallon of water in a cup of tank water and gently pour it in the tank. Perform partial water changes after 10-14 days to reduce salt content.
Updated on September 24th, 2025
Health & Wellbeing
hi... i need help and fast... i recently bought a black moor goldfish and another type of gold fish. and my black moor has what looks like on his/ her cornea a fungus? something. its white and on both eyes, and on the side of him/ her. i am worried a
Check the water chemistry first. Elevated ammonia levels may result in a cloudiness to the eye(s). Use a master test kit (liquid, not strips) at home or submit a water sample for testing. Most pet stores will do this for free or for a small fee. Perform partial water changes daily, in indicated, to stabilize chemistry and maintain water quality. Use only aged/conditioned water that is temperature matched to prevent stress or shock.
If chemistry is fine, it could be bacterial infection. A broad spectrum antibiotic, such as kanamycin, can be used for treatment. Look in the local pet store or Petco for "KanaPlex". It should be in the aquarium section. Follow label directions carefully and remove the carbon filter insert during treatment.
Plain aquarium salt (NOT table 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 of tank water and gently pour it
Updated on September 24th, 2025
Health & Wellbeing
My goldfish's tail is damaged. The fin looks bitten off as there are exposed spines where the tail fin should be. There is also a red color that looks to be blood on the base of the tail, as well as the side of the dorsal fin close to the tail. It is
By your description, it could be fin rot and a bacterial infection. Clean water is key in treating any infection. 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. Treat for 10-14 days then reassess fin condition. More water changes can be done afterwards to reduce salinity.
Updated on September 24th, 2025
Health & Wellbeing
Two of the fish fins are clamping down close to their body. I did 75% water change and hopefully they will get better. I do not have the water testing kit. Will buy soon. Is there any ways to get them better? I could see some of their scales are off.
Goldfish need powerful filtration. Your filter should be rated for at least twice the tank volume. Once you get a test kit, check the chemistry. Aim for 0 ppm ammonia and nitrites with nitrates at about 40ppm. Use a kit that has liquid reagents, not strips. The liquid kit is more accurate. The pH should range between 7.2-7.6. Being cold water fish, goldfish thrive between 65F and 72F. You can dissolve 1 teaspoon of plain aquarium salt (NOT table salt) per gallon of water to use as a general tonic. It will reduce stress, improve gill function, treat minor infection and aid in recovery. Treat for 10-14 days then reassess the condition of your fish. When performing partial water changes, treat only the volume of water being replaced not the entire tank volume. Change no more than 30% of the volume at a time. Use only aged or conditioned water that is temperature matched to prevent stress or shock.
Updated on September 24th, 2025
Health & Wellbeing
Hi there! Having a few questions: i dont know what is happening, all of our fishes are always dieing. I would like a fish expert answer. What is happening to these blue fishes? On their skin there are multiple grey spots, and another fishes are getti
Check the water chemistry. The discoloration could be due to elevated ammonia levels which can cause "burns". 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.
The Neons (blue fish) appear to be infected with Ich, a parasite. Treatment is possible with commercial products found in the local Petco. Follow label directions carefully. You will need to treat the entire tank until all traces are gone.
Removing a lump from your fish on your own is never recommended. You can cause severe injury. Most broad spectrum antibiotics (Kanaplex, Maracyn, Maracyn 2, etc.) found in the aquarium section of the local Petco should help treat or prevent infection. Choose one and follow label d
Updated on September 24th, 2025
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