Hi everyone. Ive had a DG (named Tommy) for about 5-6 weeks and over the past several days, he has gotten really sick. I think the sickness was caused by ammonia levels of around .25ppm over the course of 3-4 days. Yesterday I did a 40% water change and introduced some established filter media from another tank and I tested the water this morning and then again this evening and ammonia and nitrite are both zero. PH is around 6.8. Water temp is 77-78 F. The day before he started to get sick, he was swimming his typical DG pattern back and forth across the back of the tank and also eating really well. Then the next day, he stopped eating and just kind of hung out near the surface. The next day, I noticed that his head had started to change color - it was weird, it almost looked bruised. Then yesterday, he started spending most of his time on the bottom - obviously having trouble swimming and only doing so to get to the surface for a gasp of air. Today, his head is almost completely dark grey and he has developed a sore on top of his head. Here are some pics: What do you guys think? Does he have a chance or should I humanely put an end to his suffering? Oh also forgot to mention. He is in a 37 gallon tank along with 2 Platys and a Rubber Lipped Pleco.