Recently bought a delta tail. Didn't realize bettas needed a heater so he was living in the tank a week before I got one. He's developed red spots all over the edge of his white tail which I didn't notice until I changed his 2.5 gallon tank. The hot pink gravel made it difficult to see in the tank. Can anyone tell me what is wrong? I'm assuming its some kind of bacteria. What can I use? He hasn't been eating or swimming. Just hangs out attention top next to the heater, which is at 78 degrees.