1. Check the water temperature: Tropical fish need proper water temperature to live and swim normally. If the water temperature is too low, it may cause the fish to be stiff and unbalanced. You can check whether the water temperature is suitable for your fish and adjust it accordingly.
2. Check the water quality: Poor water quality may have a negative impact on the health of tropical fish, causing them to sink to the bottom. You can check whether the water quality is suitable for your fish, and consider changing some water or using suitable filters to improve the water quality.
3. Check whether the fish is sick: If your fish bends and sinks into the bottom of the water, it may mean that it is sick. Common diseases include imbalance, swim bladder injury, brain lesions and so on. You can check the appearance and behavior of fish, and search for related symptoms and treatments.
4. Give enough space: Tropical fish need enough swimming space. Too little space may limit their activities and cause them to sink to the bottom of the water. You can consider moving the fish to a larger aquarium or fish tank to provide more swimming space.
5. Adjust the feed: If your fish are malnourished or eat inappropriate feed, it may cause their bodies to bend and sink to the bottom. You can try to adjust the type and quantity of feed to provide more comprehensive nutrition and ensure that your fish get enough nutrition.
If your fish is seriously ill or the above suggestions can't solve the problem, it is recommended to consult a veterinarian or a tropical fish expert as soon as possible for more detailed diagnosis and treatment suggestions.