Why is my betta so lazy? Is he sick?

[SC]

Ok, so I have been asking so many questions, but I just don't know what is going on. Why is my betta so miserable??

Backstory: Was in 1 gallon tank, no heater. Was really unhappy and cold. Stopped eating, was darting around, gasping for air, pale,. Bought him a 2.5 gallon tank with a 7.5 watt heater, water is about 78 always and I even bought him a real plant. Since I got him in April, I have been using tap water, but I was keeping it in bottles to dechlorinate, but since the bigger tank, I used half bottles and then abourt 2 liters tap water and treated it.

I went to the pet store and they said he my be sick and suggested an antibiotic, He is no longer darting around, or gasping. Still pale, not eating, and lethargic. He is on his 3rd day of antibiotics, Maracyn. I don't know what else to do. He used to be so active
I have bought other food. I have two different types of pellets and a flakes. He won't eat any of it.

All of the research I have done has said it's good to understand that bettas prefer a non-fluctuating temperature in the mid-to-high 70

[AlyR]

I would get a lot of different food and when ever he stops acting sick, then you know it was the food.