Kept in a freshwater aquarium, shelled animals such as snails, turtles, crawdads and shrimp need supplemental calcium to ensure their shells stay healthy. Thin, splitting or cracked shells are clues that your hard-shelled pet is suffering from calcium deficiency. While commercial calcium supplements are available at your local pet store, one solution to your critter's calcium woes is as close as your refrigerator.
Crack Some Eggs
There is no harm in putting fresh, clean eggshells in your aquarium. Rinse them well and allow them to air dry for a day or two -- or set the oven to 250 degrees, turn it off and put the eggshells on a cookie sheet inside the warm oven. Let them cool completely before adding them to the fish tank. Large, unbroken pieces of shell are easy to remove when you clean the tank, and some fish enjoy nibbling at the shells. The egg will gradually dissolve into the water over several weeks, depending on your tank's acidity levels.
Serving Up Eggshells
To increase the calcium level in your tank more rapidly, pulverize eggshells with a mortar and pestle and sprinkle the powder into the water. The smaller particles will dissolve more quickly -- but you must consider whether you'll find the white powder that settles on the gravel unattractive. Alternatively, place a fine mesh bag containing powdered or broken eggshells in the filter reservoir to raise your tank's calcium level. Do not add small pieces of broken shell directly to your tank: Snails and fish may injure themselves on sharp edges, and broken pieces can be difficult to remove if calcium levels exceed the ideal.
Consider the Alternatives
Some shelled creatures -- crawfish, for example -- need extra calcium before molting. Increase the calcium in your shelled pet's diet by adding calcium-rich vegetables such as kale and other dark green leafy vegetables. Sprinkle the dampened leaves with powdered eggshell and secure them in the tank with a lettuce clip. Other ways to increase the calcium in your tank are adding a cuttlebone or pieces of coral, or applying a liquid calcium supplement.
Testing the Waters
Calcium in excess of 500 parts per million causes the tank's pH to become acidic, causing other health concerns for your shelled pet. Don't add eggshells to your aquarium until youconfirm your water's calcium level. Calcium test kits allow you to monitor calcium levels in your tank on a regular basis, such as weekly, to maintain ideal levels to keep your pet's shell healthy.