Ok, first off sweetheart, a .5 gallon tank is really too small for him.
Unless you are doing twice a day water changes, he is probably stressed AND sick. It's hard to keep water a good temperature without a heater, but wrapping a towel all the way around it will help to slow the temperature variations in the water.
Can you give us a little more information about the fish and tank so ppl can more accurately help?
Housing
What size is your tank?
What temperature is your tank?
Does your tank have a filter?
Does your tank have an air stone or other type of aeration?
Is your tank heated?
What tank mates does your betta fish live with?
Food
What type of food do you feed your betta fish?
How often do you feed your betta fish?
Maintenance
How often do you perform a water change?
What percentage of the water do you change when you perform a water change?
What type of additives do you add to the water when you perform a water change?
Water Parameters:
Have you tested your water? If so, what are the following parameters?
Ammonia:
Nitrite:
Nitrate:
pH:
Hardness:
Alkalinity:
Symptoms and Treatment
How has your betta fish's appearance changed?
How has your betta fish's behavior changed?
When did you start noticing the symptoms?
Have you started treating your fish? If so, how?
Does your fish have any history of being ill?
How old is your fish (approximately)?
Unless you are doing twice a day water changes, he is probably stressed AND sick. It's hard to keep water a good temperature without a heater, but wrapping a towel all the way around it will help to slow the temperature variations in the water.
Can you give us a little more information about the fish and tank so ppl can more accurately help?
Housing
What size is your tank?
What temperature is your tank?
Does your tank have a filter?
Does your tank have an air stone or other type of aeration?
Is your tank heated?
What tank mates does your betta fish live with?
Food
What type of food do you feed your betta fish?
How often do you feed your betta fish?
Maintenance
How often do you perform a water change?
What percentage of the water do you change when you perform a water change?
What type of additives do you add to the water when you perform a water change?
Water Parameters:
Have you tested your water? If so, what are the following parameters?
Ammonia:
Nitrite:
Nitrate:
pH:
Hardness:
Alkalinity:
Symptoms and Treatment
How has your betta fish's appearance changed?
How has your betta fish's behavior changed?
When did you start noticing the symptoms?
Have you started treating your fish? If so, how?
Does your fish have any history of being ill?
How old is your fish (approximately)?