I attached a picture. The one on top is him about 2 weeks ago. The bottom two pictures are from today. I noticed his one back fin (caudal fin) worn away a little..could this be fin rot? (ps. you can see it better in the last picture) should i add some aquarium salt??
Also his fins have been getting darker since i first purchased him.
I've been adding 2 drops of prime to the water as it is a 1 gallon tank and doing 100% water changes weekly. Should I be doing more? I also have it heated but it only stays around 76 with the heater I bought :/