Some people want to know if it’s safe to add sea shells to their aquariums. The answer is yes, but you should be aware of some things before you place the shells into the water.
For saltwater aquariums, sea shells are fine. You should, however, clean the shells thoroughly beforehand. There are nooks and crannies in most shells that can harbor bits of organic material. It’s best to boil them for a five to ten minutes to kill off any bad bacteria and remove any other things that could affect your tank.
For freshwater aquariums, you need to be more careful when adding those sea shells. You definitely should boil them as above. You may also want to soak them for a few hours, then change water, and repeat this several times. Since sea shells contain calcium, they will increase the PH of the aquarium water over a long period of time. For this reason, you should also use only a few shells in any one tank.
Sea shells can add a nice touch to any aquarium, and with the above precautions taken, will do no harm to your fish.