Caring for fish in an aquarium is an ongoing process that includes several important steps to maintain the health and well-being of the fish. Here is the guide to proper treatment:

1. Daily tests
Checking the fish:

Look at the fish to make sure there are no signs of illness such as discoloration, difficulty swimming or unusual behavior.
Water tests:

Check water quality by using test systems. Levels of pH, ammonia, nitrites and nitrates should be checked.
2. Cleaning the aquarium
Water change:

Change 10-20% of the water once every two weeks to maintain the water quality. This helps to reduce toxin levels and maintain a healthy environment.

Filter cleaning:

Clean the water filter according to the manufacturer's instructions. Good filtration is critical to maintaining clean and tidy water.
Cleaning the bottom of the aquarium:

Use a skimmer to clean food residue and organic matter from the bottom to prevent contamination.
3. Proper feeding
Suitable feed:

Feed the fish an appropriate amount, two to three times a day. Make sure there are no food residues after feeding.

Types of food:

Use a quality food that is suitable for your fish types (such as frozen pieces, cubes or powder).
4. Maintaining temperature
Heating:

If you have tropical fish, make sure the heating is on and maintains an appropriate temperature, usually between 24-28 degrees Celsius.
Changes in temperature:

Avoid sudden changes in water temperature, as this can stress the fish.
5. Treatment of diseases
Signs of illness:

Watch for any signs of illness, such as spots on the skin, difficulty swimming or irregular eating. If you notice such signs, contact a specialist or pet store for advice.
Treatment:

In cases of illness, you can use suitable medicines that are available at pet stores. It is important to follow the instructions for use.

6. Maintaining the balance of the aquarium
Plants and decorations:

Add plants and decorations to the aquarium to provide a hiding place for the fish and maintain a natural living environment.
Variety of fish:

If you plan to add new fish, make sure they are compatible with the environment and the other fish in the aquarium.
7. Monitoring and response
Documentation:

Keep records of water tests, water changes, feeding and disease treatment. This will help you understand the behavior patterns of your fish and identify problems in time.
Professional advice:

If you have any questions or problems, don't hesitate to contact an aquarium specialist or pet store for guidance.
Summary
Caring for fish in an aquarium is a task that requires patience, attention and commitment. With proper care, you can enjoy a healthy and beautiful aquarium with happy and healthy fish.