2. The fish in the picture got loose scales (also called vertical scales and pine cones), which were mostly caused by too great changes in water quality and water temperature. It depends on the situation that the swelling is not too big. Isolate it in a small container, stop eating, add a little yellow powder (about the amount of pellet feed for two small fish), and change the water and medicine every day. It should be able to recover in 2-3 days.
3. The eyes and body of guppies turn black, which is mostly a water quality problem. Simply turning black does not matter, and no medicine is needed.
4, the rotten tail depends on the situation, if it is the tail handle or even the body is white, throw it away. If it is pre-tail burning or traumatic tail rot, there is still a cure for tail cutting: gently pinch the front of the fish with a handkerchief or the like, cut it quickly, and cut off the rotten part in parallel. Pay attention to stop eating for one day before cutting the tail. After cutting the tail, put it in salt water with seawater concentration for rest 12 hours, and put it back in the vat after it is normal.
5. Most of your situation is caused by changing water. Usually, pay attention to changing water regularly. It is best to expose the changed water to the sun for two days. When changing water, it must be slow, and it is possible to use filter drops. Usually, don't feed too much at a time, and you can finish it in a few minutes. Too much residual bait and excretion will spoil the water. It is best to prevent fish diseases of small tropical fish, similar to pine scale disease and body ulceration, which is difficult to treat. Because it is a three-point poison, it is not easy to take the dosage, but it will be counterproductive.