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The most common cause of cloudy eyes is poor water quality, allowing certain bacteria to flourish. I suspect that you maintain good water quality, but just in case, before beginning treatment, double-check your water numbers. The strips you dip in the water are inaccurate. To get good numbers you need to use a test kit with test tubes and chemicals you add to water samples. Test kits sometimes label certain amounts of ammonia and nitrites as 'normal,' but they really aren't. Both ammonia and nitrites need to be at zero for bettas. Tiny amounts won't kill them, but they can weaken the immune system, leading to infections and difficulty treating infections.
If all the water parameters are fine (and from what you have described, I think they will be), you can treat in one of two ways. The mildest treatment is simply to add aquarium salt (available at pet stores) to the tank according to package directions. Sometimes with perfect water and salt, a cloudy eye infection will clear up. You can also use Melafix, which is sold in most pet stores. It is a very mild antibacterial medication. It is safe to use it along with salt. After using one or both of these mild treatments, if you don't get results, you can try an antibiotic called myxazin. It is strong.
Bacterial infections are th e most common cause of this, but I want to mention some other possibilities. An injury could be responsible. In that case, the condition is probably permanent. Another possibility is a tumor behind the eye.putting pressure on it. Again, there would be no treatment. Sometimes an eye actually dries up and dies. A fish can adjust to that. Fish also adjust to blindness quite well. However, since Fabes isn't eating, this situation is probably more serious. One other thing we need to consider is his age. If he was an adult when you got him, we have no idea how old he is. Some breeders sell their older fish just to get rid of them when they near the end of their usefulness for breeding. We often see betta life expectancy listed as up to 5 years, but in reality, most live 2 to 3 years. If Fabes eye condition is related to old age, treatment probably won't help. But that doesn't mean we can't try.
I would test the water, add aquarium salt, and add MelaFix. Try holding food right in front of his mouth to try to get him to eat. If you have more questions, just let me know. I hopes Fabes will be able to recover.
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