Will a sea shell harm your fresh water fish?

Yes, sea shells can harm your freshwater fish. Sea shells are made of calcium carbonate, which can raise the pH of your freshwater aquarium. This can make the water too alkaline for your fish, and can cause health problems such as fin rot and gill damage. In addition, sea shells can also release harmful toxins into the water, such as copper and zinc. These toxins can be fatal to your fish. If you are thinking of adding sea shells to your freshwater aquarium, it is important to do your research first and make sure that they are safe for your fish.