You might notice that with every day, your betta seems to be getting paler or even with daily feeding your fish gets skinnier. These are signs of an aging betta. Your betta will flare with much less gusto than it used to when it get old. After so many years, many bettas lose the enthusiasm to flare.  Also, while a healthy adult betta will swim around vigorously in its tank, old bettas will hide behind plants and décor and swim sluggishly. When feeding your betta, watch it to see how quickly it spots its food. Old bettas may swim slowly to their food and miss it a couple of times before spotting it. Old bettas tend to have "cataracts," which are filmy or hazy spots inside the eye. This is normal for old bettas, and will happen no matter how big the tank you have is or how clean you keep the water.

How would you rephrase that briefly using Vietnamese?
Quan sát các thay đổi trên mình cá. Nhận biết sự thay đổi về sức lực. Quan sát dấu hiệu xuất hiện cườm khô trong mắt cá.