Slate is a natural stone that is commonly used as decoration in fish aquariums. The stone does not alter the pH of the water, and can provide hiding places for fish. Fish owners can use slate found at any home improvement store, but there are steps you must take to prepare the stone for the aquarium. These preparatory steps will make the slate safe for your fish and the aquarium water.
Wipe down the piece of slate with a clean cloth to remove any dust. Inspect the slate for any glittering, metallic spots. Look for holes or cavities in the slate. Avoid using the slate if you find these things because they are signs of mineral deposits that may leach into your aquarium and kill your fish.
Scrape a fingernail across the surface of the slate. Discard the slate if rock residue scratches off because the slate may dissolve minerals into the water.
Drag a metal file along any sharp edges or pointy spots on the slate. This dulls the edges so they will not cut the fish.
Fill a bucket large enough to submerge the stone in with water. Place the stone in the water so it is totally covered.
Leave the stone to soak for one week. Change the water in the bucket once a day. Remove the stone from the bucket and lower it into your aquarium.
Remove the stone when you change the aquarium water. Rinse it in cool, clean water and gently wipe it with a sponge to remove any fish waste material.