Insten Aquarium Fish Tank Gravel (Grey) Siphon Vacuum Cleaner.

Aqua Culture Aquarium Gravel (Grey), White Chips, 5 Lb.
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Onyx Gravel - Seachem, USA - naturally source fracted substance; appears to be porous clay or rock; very hard; light and dark grey; resembles large aquarium gravel; 2-10mm in size; no organic matter.
Fish Tank Gravel 1 Kg Aquarium Gravel Black Grey White Polished Stone 2-3 mm in Pet Supplies, Fish & Aquarium, Gravel & Substrate | eBay
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An aquarium doesn’t have to have gravel or sand, but for appearances, giving your animal a more natural setting, and a place for harboring beneficial bacteria, most aquarists buy substrate. Aquarium gravel is not that expensive to begin with, but there is a cheaper alternative for those buying in bulk. Pea gravel is often used for landscaping, but it is safe for aquariums. A lot of stores, like Menards and Lowe's, will have pea gravel; compared to the weight and cost ratio, you are getting more for your buck than in pet stores. So if setting up a natural-looking environment, pea gravel is definitely the way to go; the gravel is earth-toned with a mixture of off-white, brown, and grey pebbles. Aqua Culture Ocean Beach Aquarium Gravel (Grey), 5 lb.
Photo provided by FlickrEstes Gravel (Grey) Special Spectrastone Aquarium Gravel, Dark Blue, 25 lb/ ..
Photo provided by FlickrEstes Gravel (Grey) Spectrastone Aquarium Gravel, Blue Jean, 25 lb/Bag.
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A Mystery Snail is a often available in pet stores. A Mystery Snail shell is generally brown in color, although other Mystery Snail shells can be creamy white. Mystery Snail shells can be a solid color, have a color gradient, or have accents of light brown, dark brown, black stripes and other markings. Mystery Snail shell color variations and patterns are virtually limitless. A Mystery Snail head and body are generally dark grey or black, with its foot being a lighter gray. Mystery Snail body colors can also range from yellow, gold, blue, green, brown and purple.A Mystery Snail body is spotted with orange dots sprinkled across its head and body, providing an intriguing accent color. Orange accents also appear across the top portion of its mouth, as well as on its tentacles and siphon. On the tentacles and siphon, the orange accents appear more like lateral dashes as opposed to round spots. Black dashes also appear on its siphon. A Mystery Snail has orange rings appearing around its eyes, where their eyes rest on the tip of their eye stalks. A Mystery Snail also has an operculum that serves as a “trap door” used to seal itself in its shell.Most questions regarding Mystery Snails come from the following areas:As with any aquarium purchase, avoid buying Mystery Snails from tanks with dead or dying snails, fish or other tank mates. Tanks with dead or dying inhabitants may indicate sickly conditions, poor water quality or contagious diseases. It’s better to avoid these issues instead of getting involved with them.When buying Mystery Snails, look for snails with thick, non-pitted, non-cracked shells. Having thin, excessively pitted or cracked shells may be evidence the snail is unhealthy. It can also mean the snail has been in acidic water long enough to dissolve the shell and weaken it. And make sure the Mystery Snail shell does not have holes.Look for Mystery Snails that are stuck on the aquarium glass or moving across hard surfaces. If Mystery Snails are laying still on the bottom of the tank, laying upside down or floating on the surface of the water, it may indicate the Mystery Snails are dead or dying. Finally, keep in mind that Mystery Snails can be kept in stores with tank mates that may bite off their tentacles, eye stalks and siphon. So make sure the snail looks healthy, complete and intact before selecting.Mystery Snail Shell Size: In the display tank, a Mystery Snail shell size can be about two inches in diameter. Some snails may be smaller, or some a bit larger, but two inches around is probably most common. Larger shells are not necessarily healthier snails.