Hello everyone, here is my story: I have a betta fish, named Louis, since 4 month ago.(don't know his exact age but I assume that he is adult since he's not grow any larger) At beginning, I house him into a glass bowl that hold about 2 gallons water, no heating, no filter,no light, just a plain bowl, with some substrate and fake plants decoration. I did this because I did some research and people saying betta will do fine in just a bowl.(Now I know this is not correct since betta do need a filter and heater.) In fact, Louis did Very good when he stay in that bowl. He swims around, eat like a little pig, (I don't over feed fish), and the color on his tail is AMAZING. I guess the reason is that I always keep my room temperature to 80F and do the 50% water change twice a week. The true story starts here: 1 month ago, I realize that I should give him a more comfortable house and I rehouse him into a 10 gallon tank. Here is the picture that taken on the first day he got to his new place: The tank was running for like 3 month and fully cycled. No tank mates, with a heater, filter and LED light that good for a 10 gallon tank. I stick on my PWC schedule ( 25-30% a week) on that tank and always use dechlorinated water, and add bacterial supplements on each water change. (At this point, I assume that I have done everything correct). BUT, things are changed: His color become pale during this month and the tail start showing red dot, recently, his tail is even ripped off. He is not happy as before, he is not swimming around and sometimes he will spit out the food. He just keeps stay at bottom. Here is the picture that taken today: I realized he may be sick, here is my question: 1. why he get sick when the environment is getting better? and why he was fine when the environment seems not good? 2. how can I cure him? now I have a quarantine tank, (2.5 gallon and every basic equipment for it). aquarium salt, pimafix. I am hesitate to buy any antibiotic medication since it may harm the fish. Please, any responds will be appreciated. I love him so much and don't want lose him. THANKS!