What are the best medicines for fish parasites, bacteria, or fungus?

Without an image, it is difficult to make detailed recommendations. In general, maintain pristine water quality and chemistry. Monitor for elevated ammonia or nitrite levels and perform partial water changes as needed. Use only conditioned water that is temperature matched to prevent stress or shock. Consider adding in a second antibiotic, such as Kanamycin, to treat gram negative bacterial infection. When treating the tank, be sure to remove the carbon filter insert during treatment.

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.

Metronidazole is used as an antibiotic against anaerobic bacteria in aquaria as well as an antiprotozoal medication. Dosing will depend on the concentration of the product as well as the size of the tank. Follow label directions carefully and remove the carbon filter insert during treatment.

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.

If you have an activated carbon filter insert, remove it or it will filter out the medication. Confirm adequate water quality and chemistry since both can impact health and healing. Consider adding a broad spectrum antibiotic to treat infection. You can purchase products such as Kanaplex or Maracyn in the aquarium section of the local pet or fish store. Follow label directions carefully. Plain aquarium salt (NOT table or Epsom salt) can be used at 1 teaspoon per gallon of water to reduce stress and aid in recovery.

If you have another tank, it will make treatment easier. It will also preserve beneficial bacterial populations in the main tank since antibiotics may be used. The cornerstone of treatment and recovery is pristine water quality. Keep the water as clean as possible via filtration and regular partial water changes. Use only conditioned water that is temperature matched to prevent stress or shock. You can find a broad spectrum antibiotic in the aquarium section of the local Petco. Follow label directions carefully and remove the carbon filter insert during treatment if indicated. Once the fish has recovered, you can return it to the main tank. If you don't have a "hospital" tank, you can treat the main tank.

Consider a broad spectrum treatment such as General Cure by API or Parasite Clear by Jungle Labs. Follow label directions. Plain aquarium salt (NOT table salt) can be used concurrently to aid in healing and to treat minor infection and fin rot. Dissolve up to one tablespoon per gallon of water into a cup of tank water and gently pour it into the tank. Test water chemistry using a home test kit or submitting a water sample. Most pet or fish stores will do this for free or for a nominal fee. Correct any imbalances using aged or conditioned water that is temperature matched to prevent further stress or shock. Use a conditioner such as StressCoat as well. Confirm adequate filtration to maintain water quality.