Constipation causes fish to float on their sides. Deshelled peas (any variety) contain enough fiber to make them regular again. If your fish hasn't had a bowel movement in the past few days, feed them two to three fresh peas or thawed frozen peas each day. Mash them or let the chunks float to the bottom of the aquarium.  Avoid canned peas, as they contain sodium and spices that can hurt your fish. Soften the peas. You can do this by boiling them on the stovetop in filtered water for one minute. Allow them to cool down after you remove them from the  pan. Don't use a microwave, since this can destroy vital nutrients. Remove the skin by peeling it off with your fingers. Make sure you wash your hands first! Cut the peas into small pieces. First, cut them into halves if they didn't split naturally when you peeled them. Then, cut them into quarters. If your fish is small, cut the pieces even smaller. If your fish isn't constipated, they might have eaten too much. Overeating can cause a fish's stomach to bloat and force them to float on their sides. If your fish has had a recent bowel movement, don't feed them for three to four days. When fish sleep, they stop moving. For example, betta fish and goldfish sleep by resting on the bottom of the tank. Search online and read books about caring for fish to learn about your fish's sleeping habits.  Search for this information on veterinary websites or at your local vet's office. Visit your public library or pet store for informative books. If you have access to scholarly databases, search for articles in veterinary journals. Some fish like to play dead just to see you freak out. Be sure to double-check Chlorine, chloramine, and heavy metals in tap water can sicken and kill fish. Add water conditioner to the aquarium, following the instructions on the packaging. You can buy water conditioner at your local pet store.  Test your tank water for chlorine, chloramine, and heavy metal before adding conditioner. You can buy testing kits at your local pet store. Follow the...

TL;DR in Vietnamese:
Điều trị táo bón bằng đậu Hà Lan. Giảm lượng thức ăn khi cần thiết. Nghiên cứu về cách ngủ của cá. Tình trạng nước trong bể cá. Kiểm tra nhiệt độ nước.