I have two guppies in a freshwater tank. One of my guppies is fine and healthy but my other guppy is much smaller and hasn’t eaten in the past 24 hours. He is at the top of the tank, like there isn’t enough oxygen and he is gasping, however my other fish is fine both at the top and the bottom of the tank and I have the filter and an air pump running so I don’t think oxygen is an issue. As I mentioned before he hasn’t eaten but more importantly his tail has started to deteriorate extremely quickly and the top half is almost completely gone, he has to use his two front fins to move himself around and struggles to stay up. Is there anything I can do to help him?