I’ve been out of town for five days (husband has been caring for animals) and returned this AM to find my betta sitting on the bottom with a lump/tumor on his side near his tail and one enlarged eye. He came up for food and is swimming around now. He has one mystery snail as a tank mate. Water parameters were fine (0 ammonia, 0 nitrites, 50 nitrates, temp 81, pH 7.4) but I did a 60% water change anyway. Please help!