I am a college student and studied abroad this past semester, so I left my boy in my parents care for the past four months. I instructed them how to care for him and the tank before going but I just landed and it’s clearly been neglected. He is pineconing, extremely swollen, and can barely swim. They told me the swelling started about a week ago, so I don’t know if it is too late to save him (they decided not to tell me about it because I had finals :/ ). He also has a tumor on his left side that is shown in the first photo, which also makes me worried if treatment will work. I don’t know if at this point I should try to treat him or if it is most humane to euthanize. Treating the tank itself is also going to require a lot of time.
Water parameters are shown in the last photo, ammonia ~0.25, nitrite 0, nitrate ~5.0. It’s a 7 gallon tank, kept at 78°. There is a lot of algae and diatoms and it looks like there is CB on the rocks as well. The filter media was so clogged with brown mush that there was virtually no water circulation. They said they were doing 10% water changes every 5 ish days. I know I should have checked in more to make sure the tank was okay but they kept saying it was fine :(
Please help!!