Summarize this article in one sentence.
Most fish illnesses can be addressed by thoroughly cleaning and disinfecting the tank. With all of these conditions, try this approach first, and then move on to medications if you don't see improvement. Keep track of the symptoms in case you need to consult an aquatic veterinarian to treat your fish. Immediately remove a sick fish from a tank. A fish that has a fungal infection will be paler than usual, will not be active, and will have clumped together fins. Most noticeable will be the white, cotton-like patches on its body. Eliminate a fungal infection by cleaning the tank and treating fresh water with fungus eliminator. Repeat every three days until visible signs of fungus have disappeared. Treat the water with BettaZing or Bettamax to dissolve any remnants of the fungus. Fungal infections are typically the result of a tank that has not been properly treated with salt and Aquarisol. Fungal infections are highly infectious, so this disorder should be treated rapidly. Quarantine infected fish. In this case, your Betta fish's fins and/or tail will turn black or red along the edges. The fin will appear to be dissolving and getting shorter. You might see holes or tears in the fin. Clean the tank once every three days. Add either Ampicillin or Tetracycline into the water to treat it. Repeat until your fish's fin ceases to show signs that is still losing tissue. Put some fungus eliminator in the water to facilitate recovery. The tail will repair itself over time, but might not obtain its original luster. If not treated, this condition can progress to the point where it begins to eat away at your fish's body. Ultimately, it will be fatal. If the belly of the fish is enlarged, the fish might have some blockage that needs to be corrected. You might notice an absence of excrement in the tank. The fish might have trouble swimming upright, swimming instead on its side or even upside down. This is a sign of overfeeding. The condition can easily be treated by reducing how much you feed your Betta fish. Your fish will have white dots all over its body and will lack appetite. It will also try to scratch itself against items in the tank. It is highly contagious and is the most common cause for fish fatalities. To treat ich, you should raise the temperature of the tank to somewhere between 78 and 80 degrees Fahrenheit over 48 hours. Add formalin or malachite green to the water. Fish with Velvet will hold their fins against their body, lose color, refuse to eat, and scratch against the gravel of the tank. It is treatable, but can be hard to spot. To verify that your fish has Velvet, shine a flashlight on it and check for a light gold or rusty film over its skin. Treat Velvet by cleaning the tank and treating the new water with BettaZing. Velvet should not occur if you have been treating your tank properly with salt and water conditioner. If your fish contract Velvet you should reconsider how you care for the tank. If one of your fish's eyes is budging out, then it has pop-eye. Unfortunately, pop-eye is not caused by a single condition. Sometimes it is treatable, but other times it is not. If several fish exhibit signs of pop-eye, the water condition is likely at fault. Test the water and replace 30% of the water daily for 4 to 5 days. If one of the fish has pop-eye, it might be a bacterial infection. Remove the fish to a separate tank and treat with Maracyn or Maracyn II until it shows signs of improvement. Occasionally pop-eye is the result of a serious, untreatable medical condition. If your fish does not respond to treatment it is possible that nothing can be done for it. In cases of dropsy, your fish's stomach will begin to swell. When it swells, it will cause the scales to project out like a pinecone. It is not a specific illness, but a sign that your fish can no longer regulate fluids. It will be fatal. If caught early, dropsy can be cured by aquarium salt baths and medicines. However, since it is hard to see what kind of medicine to use (the wrong one can make it worse), this is hard. Vets can help. If the betta is severely affected, euthanizing it is an option. Dropsy is not contagious, but it could be an indication that your water parameters are off. Check them and consider replacing your water. An aquatic veterinarian is one that specializes in treating fish. They are not as common as vets who treat cats, dogs and other household pets.

Summary:
Begin with water and food. Treat a fungal infection. Treat tail or fin rot. Treat swim bladder disorder. Treat ich. Treat Velvet. Treat pop-eye. Check for dropsy. Consult an aquatic veterinary specialist.