Warm moist environments can be a breeding ground for mold, which is not suitable for people with breathing problems. Most tropical fish live in warm and moist environments. While fish tanks may not directly cause problems with breathing, you will need to follow a rigorous and regular water change routine to tackle the mold growth issue. It is also advisable that people with breathing problems abstain from sleeping in the same room where the aquarium is placed.   Always make sure to keep the fish tanks clean and healthy so that you and the fish are in the best of their health. If a healthy cleaning routine is followed, people are less likely to get sick from owning these finned companions. You will be benefitted by the positivity these marine creatures can bring to your home.