Hello. Tuesday I noticed my betta seemed bit a lethargic so I decided to completely replace the water and give it fresh clean water. After that he seemed to get worse. He has been very lethargic and labored breathing. He has been laying at the bottom sideways and kind of curved. Sometimes he stays kind of straight at the bottom. Looks like he does does have some mild fin rot. I am worried. I have had him for 2 years now. It has been about 2 days now and he doesn't seem to get any better. I thought of buying metafix but I have seen negatives reviews on it. Fish tank temp is around 78-80 degrees. I do have some betta salt but I did not add any. Any advice what could my fish's problem is? What can I do to help? Please help.