my betta has an enflamed eye!

[kaos]

Hello,
I've only recently noticed this but my betta fish seems to have an enflamed eye now. The area around his left eye is quite swollen compared to his right eye and I haven't the slightest clue as to why this is.

I've had him for about 1.5 years now, and he's been in his small 1 gallon-ish tank ever since. I use tap water and conditioner in the tank. He is eating, swimming around and overall seems quite healthy.

If anyone knows what this might be, any information would be much appreciated. Thanks.

[Lupin]

Welcome to Fishforum.com.

I would like to know your water parameters. How often do you replace the water? How much water volume do you replace?